Category: TumbleStoneTwo

This Series of Posts provides an introduction to Gemstone Beach (Orepuki, Southland, New Zealand) and a basic guide to many of the stones commonly found on that beach. Previous Posts = Part One: Location and Carpark; Part Two: Main Features of the Beach; Part Three: Sources of Information & What is a Gemstone; Part Four: Brief Introduction to Geological Terms for Stones; Part Five: Translucent Stones; Part Six-A: Stones that are Predominantly White; Part Six-B: Stones with White Spots & Crystals; Part Six-C: Stones with Opaque White Veins & Bands.

The previous three Posts looked at seven types of white stones, or white parts of stones, that can be found on Gemstone Beach: 1 – White Milky Quartz Stones; 2 – White Hydrogrossular Garnets; 3 – White in Other Coloured Hydrogrossular Garnets; 4 – Stones with Opaque White Spots; 5 – Stones with Opaque White Crystals; 6 – Stones with Opaque White Veins; and 7 – Stones with Opaque White Bands. This Post looks at 8 – Stones with Opaque White “Patches”. There could be other types of white stones on Gemstone Beach but these are the ones I am currently aware of that are most likely to be found.

8 – STONES WITH OPAQUE WHITE “PATCHES“

This section contains a wide range of stones with opaque white material in them. Some have white patches in a conventional sense, others have a variety of white material and shapes. I have struggled to organise the stones in some sort of logical sequence or set of categories, so they are set out in a rather haphazard way. I also don’t always know the identity of a mineral or stone. What I hope this section will do is encourage you to look more closely at a stone you pick up on Gemstone Beach, to see how it is made up of a variety of colours, patterns and minerals.

Sometimes a stone looks like it has a little white in it but closer inspection suggests that the whole stone is likely to be white originally but then it has been “flooded” with a colourful mineral; or maybe the white is the matrix for fragments of a colourful stone (a breccia):

Stone W117, quartz with iron oxide through it?

Stone W118, iron oxide mineral in white quartz, or breccia stone?

Stone W119, white quartz with green epidote mineral through it?

Stone W120, white and transparent stone with green mineral in it.

As mentioned in the previous Post, a “breccia” stone (like Stone W118) consists of small angular fragments (clasts) of one or more rocks cemented together in a fine-grained matrix. The small fragments come from some form of erosion and their angular shape means they have not “travelled” far, they have not had the chance to be smoothed. A similar type of stone with rounded smooth fragments is called a “conglomerate”. A number of the stones shown below are also likely to be breccia.

Stones W121 and W122 below are white stones with darker and/or colourful areas – the former at first glance looks as if some small areas of minerals are in it but closer inspection suggests it may be, like Stone W122, a breccia stone with opaque white quartz being the matrix:

Stone W121, white and other colour areas – breccia?

Stone W122, breccia stone with matrix of opaque white quartz.

The next two stones have black and white “patches” but the shapes and mix of the contrasting materials are very different – both have very interesting detail:

Stone W123, white and black mix.

Stone W124, white and black mix.

Another two breccia, both with white fragments (clasts) but one with a light green-coloured matrix, the other with a brown matrix:

Stone W125, breccia with white clasts.

Stone W126, breccia with white clasts.

Some of the stones I have found on Gemstone Beach have “hints” of white and closer inspection is needed to see their patterns more clearly:

Stone W127, hints of white.

Stone W128, hints of white – quartz flooded by iron oxide?

Stone W129, white patchwork, maybe a breccia?

Maybe Stones W127 and W129 (above) are breccia and Stone W128 is quartz “flooded” with dark red iron oxide. Stones W130 and W131 (below) have “wedges” of white material but their details are very different – Stone W131 has a very interesting margin along the edge of the white:

Stone W130, wedge-shaped areas of white.

Stone 131, wedge-shaped area of white.

Below is a selection of five other stones with white “patches” in them, again illustrating a diversity of colours and patterns:

Stone W132, white quartz and cloud of iron oxide.

Stone W133, breccia.

Stone W134.

Stone W135, large white quartz fragment in stone.

Stone W136, bright opaque white patches, brown mineral threads.

The different ways that black and white “patches” can occur are well illustrated by the following three stones – Stones W137 and W138 are breccia but with contrasting colours of fragments, while Stone W139 appears to be a white quartz stone with black mineral inclusions:

Stone W137, breccia of white fragments in dark matrix.

StoneW138, breccia of black fragments in white matrix.

Stone W139, black mineral in white quartz?

The next four stones have small white “patches” that are part of unusual structures. Stone W140 has an unusual light green colour (the matrix), probably caused by the mineral epidote, with small white fragments (quartz?) – it is an example of a breccia where the matrix makes up more of the stone than the fragments or clasts. Stone W141 could also be a breccia but with the epidote material being the fragments – I am not sure. Stone W142, most likely a quartzite, has been subjected to stress and veins filled in the resulting gaps. Stone W143 is a green stone with gorgeous small orbs in it, along with small patches of white and transparent quartz – I’ve always imagined such orbs are created in heat flows within a cooling rock, but I also know that sometimes they arise as crystals grow within such rock.

Stone W140, light green breccia with white fragments.

Stone W141, breccia, with epidote and quartz??

Stone W142, grey quartzite with veins and white areas.

Stone W143, orbicular green stone with white and transparent quartz.

The next two stones both have what at first sight appears to be small lone bits of white. However, closer inspection reveals that Stone W144 is probably a quartz stone flooded by a dark red mineral (maybe iron oxide). And Stone W145 may be a quartz breccia(?) with a singular opaque white clast – it is tempting to call it a “xenolith” (a “foreign” stone in a stone of different material) but this term is usually used in reference to igneous rocks.

Stone W144.

Stone W145, brown stone with small white inclusion.

The final two stones with white “patches” are both green quartzites with small areas of opaque white material. This white material seems different from the white quartz seen in other stones, and may be a different mineral.

Stone W146, green quartzite with small white areas.

Stone W147, green quartzite with small white areas.

Both stones also have a number of thin veins, mainly transparent.

The next Posts in this Series (not yet all available) will look at green Gemstone Beach stones. The first one, just completed, is on green argillite stones. 

DISCLAIMER: Over the past six years I have visited Gemstone Beach more than 150 times, also walking further along the Te Waewae Bay coast. But I am not a geologist – I am an amateur beach stone collector and polisher. I have done some reading and research about different types of stones, but my knowledge is limited and open to correction. Some of the photos used in these Posts were taken at Gemstone Beach in April 2023; some come from my fossicking trips there over the past three or four years; and a few were taken after I looked through my “finds” in my stone shed at home. All the stones are “rough”, not polished. The coverage of stones is not comprehensive and is biased by my own interests and what catches my attention. The photos are not perfect, often having some reflections in them. But I hope these Posts prove useful to the “passing motorist” and others who find themselves on this interesting beach. 

Go to GEMSTONE BEACH AND ITS STONES: AN INTRODUCTION FOR THE PASSING MOTORIST – PART ONE, LOCATION AND CARPARK

Return to GEMSTONE BEACH

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A spiral of veins. Source: http://www.facebook.com/photo?fbid=10231121915935133&set=gm.1262109917830034&idorvanity=917642255610137Source:

This Series of Posts provides an introduction to Gemstone Beach (Orepuki, Southland, New Zealand) and a basic guide to many of the stones commonly found on that beach. Previous Posts = Part One: Location and Carpark; Part Two: Main Features of the Beach; Part Three: Sources of Information & What is a Gemstone; Part Four: Brief Introduction to Geological Terms for Stones; Part Five: Translucent Stones; Part Six-A: Stones that are Predominantly White; Part Six-B: Stones with White Spots & Crystals.

The previous two Posts looked at five types of stones, or parts of stones, that can be found on Gemstone Beach that are white: 1 – White Milky Quartz Stones; 2 – White Hydrogrossular Garnets; 3 – White in Other Coloured Hydrogrossular Garnets; 4 – Stones with Opaque White Spots; and 5 – Stones with Opaque White Crystals. This Post looks at 6 – Stones with Opaque White Veins, and 7 – Stones with Opaque White Bands. The next Post looks at 8 – Stones with Opaque White “Patches”. There could be other types of white stones on Gemstone Beach but these are the ones I am currently aware of that are most likely to be found.

6 – STONES WITH OPAQUE WHITE VEINS

There are lots of stones on Gemstone Beach that have white veins in them, though they may not be noticeable at first. Among them are the very common dull grey stones, such as Stone W82 below. The first three photos of Stone W82 are of the dry stone, showing a typical light grey colour, while the second set of three photos is of the same stone when wet, which darkens its colour.

Stone W82 dry, greywacke with white vein. Photo from Chrissy.

Stone W82 wet, greywacke with white vein. Photo from Chrissy.

Stones W83 and W84 are two more white veined grey stones, photographed dry. Variation in the thickness of veins is apparent. The veins are often in fact layers of white material, running right across a stone.

Stone W83, white veined greywacke. Photo from Chrissy.

Stone W84, white veined greywacke. Photo from Chrissy.

The next white veined stone is darker in colour, with a number of white veins:

Stone W85, dark sandstone with white veins.

Sometimes a white vein in a grey stone can have a rusty hue because of the presence of iron oxide:

Stone W86, greywacke with iron oxide stained white vein.

As I currently don’t have many photos of grey stones with white veins, I asked Chrissy Lampitt if she would send some to me. Chrissy lives at Papatotara, 20 kilometres along the coast of Te Waewae Bay from Gemstone Beach, and has a blog called Tumble and Polish. I first met her in March 2023. She kindly provided the photos of Stones W82, W83 and W84 above, the stones being found on her local beach. They are the same kind of white-veined grey stone as found on Gemstone Beach (and on many beaches and in many rivers in New Zealand).

The following Gemstone Beach grey stone with white veins seems to consist of finer grains and is smoother to the feel. Cross-cutting transparent veins are also present:

Stone W87, grey mudstone? with white (and translucent) veins.

The next two stones are also fine-grained and smooth, and their white rings could be either veins or bands. A “vein” is an infilled crack. When rock comes under pressure and stress, it fractures and cracks of different sizes open up. This allows hydrothermal fluids, carrying dissolved minerals, to enter the gaps in the rock. Over time, the dissolved minerals precipitate out of the hot water. Crystals, such as quartz, grow within the cracks and fill them. Often, as the stresses on the rock change their orientation over time, veins will crosscut and even overlie each other (as with Stone W87 above). For useful information on this process, see Geology Fundamentals, Wikipedia, and for a more technical account see Alex Strekeisen.

In contrast to a vein, a “band” is a layer that is an integral part of the original stone, such as a layer of differently coloured sediment in a sedimentary stone. It can often be difficult to tell veins and bands from one another. For Stone W88 below, the thin white offset lines could be very thin layers of white material deposited in sediment, and Stone W89’s thick ring could be a lighter-coloured layer of sediment as well, though it might be a vein instead – it can be difficult to tell them apart.

Stone W88, grey-green mudstone/argillite with white veins/bands.

Stone W89, argillite with white vein or band.

Note that the offset rings in Stone W88 are a result of stresses on the rock after it was formed – such stones are sometimes known as “earthquake” or “faulted” or “faultline” stones (see the second part of this Post for an example).

Stones W82 to W85 (and maybe W86) are highly likely to be greywacke, a coarse-grained sedimentary rock (a sandstone). Such stones dominate at Gemstone Beach. The following six photos are of specimens of greywacke with white veins from elsewhere, the lower three showing how imaginative and creative arrangements of veined stones can make quite effective patterns:

Greywacke stones. Source: https://teara.govt.nz/en/photograph/5121/greywacke-pebbles-with-quartz-veins

New Zealand greywacke stone with white bands. Posted in January 2021 in Facebook Group “New Zealand Lapidary, Rocks, Minerals, Fossils” by “Kween Bee”. Used with permission.

White veined greywacke stone. Source: https://rockidentifier.com/wiki/Greywacke.html

Greywacke stones arranged to create a white circle. Source: http://www.pinterest.nz/pin/133630313913580967/

Greywacke stones arranged to create a white circle. Source: http://www.pinterest.nz/pin/50665564550630710/

Arrangement of veined sandstones. Pages 80 & 81 of “Beach Stones” (2006) by Josie Iselin & Margaret Carruthers.

There are other examples of the creative use of white-veined stones further below.

Phil, a member of the Facebook Group “New Zealand Lapidary, Rocks, Minerals, Fossils” made the following comment after reading the first draft of this Post: “The majority of veins in greywacke are in fact zeolite which is a product of the depth of burial (ie: the zeolite metamorphic facies). Quartz veins are present in greywackes however, but they tend to be minor compared to zeolite.” Most of us, including me, tend to assume that all of greywacke’s white veins are quartz. Phil provided a photo showing zeolite and quartz veins in greywacke (see photo below, far left): “In the photo, the milky vein is quartz and the white vein is zeolite. The thousands of white spots are feldspars, showing the sediments for this greywacke had a volcanic origin.”

Whitest large vein is a zeolite, lighter large vein is quartz. Source: Phil in Facebook Group “New Zealand Lapidary, Rocks, Minerals, Fossils”

White zeolite (stilbite) amygdale. Source: https://blogs.agu.org/georneys/2012/10/28/geology-word-of-the-week-z-is-for-zeolite/

White vein of the zeolite natrolite. Source: https://blogs.agu.org/georneys/2012/10/28/geology-word-of-the-week-z-is-for-zeolite/

Stilbite crystals. Source: https://www.mindat.org/gm/4395

Phil also noted that you can determine whether a white vein is zeolite or quartz because of their relative hardnesses – you will be able to easily leave a scratch on zeolite with a knife, but not on quartz. Zeolites are a group of minerals with a crystalline structure made up of silicon, aluminum, and oxygen. They include minerals such as natrolite, stilbite and phillipsite.

Stones W87 to W89 above are highly likely to be argillite, a fine-grained sedimentary stone (a mudstone). More information on greywacke and argillite can be found at the end of this section, following Stone W113.

There are in fact quite a variety of different coloured stones with white veins of different thicknesses that can be found on Gemstone Beach. The following 12 stones represent a sample in order of increasing vein thickness. A wide range of different stones are involved, and often the veins themselves have unique characteristics. The first six stones all have a thin white vein:

Stone W90, red spotted argillite with thin white vein.

Stone W91, orbicular hematite jasper with thin white vein.

Stone W92, thin white vein.

Stone W93, thin white veins.

Stone W94, quartz with epidote, with white vein.

Stone W95, black and white igneous stone with white vein.

For the next six stones, the white vein gets thicker:

Stone W96, multi-veined igneous stone.

Stone W97, red sandstone with white vein.

Stone W98, thicker white vein.

Stone W99, quartzite with white vein.

Stone W100, white quartz vein.

Stone W101, thick white vein.

Some of the veins can be complex and some stones have a number of veins, some of which are white and some of them transparent. These reflect how a rock can fragment in other than a clean and straightforward way:

Stone W102, complex white veins.

Stone W103, complex white and transparent veins.

Sometimes, white veins appear to be infills of irregularly shaped crevices, as in this rhyolite and this breccia (pronounced “breh-chee-uh”):

Stone W104, rhyolite with white vein.

Stone W105, breccia with white vein.

It is possible that the white area in the rhyolite (Stone W104) is part of its “flow-banding”, being a band of white coloured minerals laid down at the stone’s formation.

A “breccia” stone (like Stone W105) consists of small angular fragments of one or more rocks cemented together in a fine-grained matrix. The small fragments come from some form of erosion and their angular shape means they have not “travelled” far, they have not had the chance to be smoothed. A similar type of stone with rounded smooth fragments is called a “conglomerate”. See this Post for more information on Gemstone Beach breccia. Photos of other Gemstone Beach breccia stones, of a variety of colours and fragment sizes, are below:

Breccia in Riverton Aparaima Museum Poster of Gemstone Beach stones.

Polished Gemstone Beach breccia stone. https://tumblestoneblog.wordpress.com/2022/01/15/january-2022-stone-of-the-day-15-dark-red-green-brecciated-stone-from-gemstone-beach/

Polished Gemstone Beach breccia stone. https://tumblestoneblog.wordpress.com/2021/05/12/fb-group-posts-2-3-4-may-2021-jasper-breccia-and-faultline-stone/

Polished Gemstone Beach breccia stone. https://tumblestoneblog.wordpress.com/2022/01/02/january-2022-stone-of-the-day-2-breccia-and-the-giant-landslides-of-fiordland/

Unpolished Gemstone Beach breccia stone, found March 2022. https://tumblestoneblog.wordpress.com/2023/03/20/southern-sojourn-202326-delightful-discoveries-desperate-de-pants-ing-and-dramatic-drenchings-on-gemstone-beach-sunday-19-march/

Next are some interesting patterns and variations of white veins in five stones found on Gemstone Beach – the first two have end veins nearly eroded away, the second of which makes a heart shape; the third (Stone W108) has a wavy line; Stone W109 has a small fore-shortened wave; and the fifth one has crisscrossing white lines :

Stone W106, jasper with white vein.

Stone W107, white vein suggesting a heart.

Stone W108, wavy white vein.

Stone W109, shortened white vein.

Stone W110, crisscrossing white veins.

The last three white-veined stones are among the most beautiful I have found on Gemstone Beach or nearby. They are rare, so are unlikely to be found easily and in a short time. Many of the white veins in the stones above have been quartz – these ones may be a form of chalcedony, often called agate. In Stones W112 and W113, the veins are transparent but have an opaque white lining. All three stones are hematite jaspers.

Stone W111, hematite jasper with very thin veins of maybe chalcedony (agate).

Stone W112, hematite jasper with transparent veins with opaque white lining (maybe chalcedony aka agate).

Stone W113, hematite jasper with transparent veins with opaque white lining (maybe chalcedony aka agate).

It is amazing what close examination of wet stones reveals on Gemstone Beach!

The imaginative and creative use of a range of differently coloured stones with white veins can be seen in the photos below. This includes the construction of circles and spirals, and the arrangement of veined stones that look like letters of the alphabet – there’s even a book, “Alphabeach”, of alphabet letter stones.

A circle of veins. Source: http://www.pinterest.nz/pin/1048986938180703715/

Twin circles of veins. Source: http://www.beachstuff.uk/stones_and_stone-like_things.html

A spiral of veins. Source: http://www.facebook.com/photo?fbid=10231121915935133&set=gm.1262109917830034&idorvanity=917642255610137Source:

Spiral of veins. Source: http://www.pinterest.nz/pin/376121006354428631/

Letters of the alphabet, in white veins. Source: http://www.pinterest.nz/pin/10414642881011278/

Letters of the alphabet, in veins. Source: http://www.reddit.com/media?url=https%3A%2F%2Fi.redd.it%2Fqac37ndrlqb61.jpg

“Hello. Who are you?” Source: http://www.pinterest.nz/pin/13370130123164306/

“Write stones”. Source: https://www.boredpanda.com/complete-stone-alphabet-swiss-alps-andre-quirinus-zurbriggen/

http://www.amazon.com/Alphabeach-Alphabet-Laura-Anne-Crowell/dp/1796079626

On Greywacke and Argillite, Common Bearers of White Veins

Greywacke and argillite are both very common in New Zealand and are often associated with each other geologically. “Greywacke” is a word of German origin, from “grauwacke”, meaning grey sandstone. As Hamish Campbell put it, in an article in “New Zealand Geographic” in 1999: “It formed from sand, mud, gravel, and silt that was eroded off existing land and dumped by rivers into the sea, there to be compressed over tens of millions of years.” In fact, greywacke is the bedrock of not only New Zealand but also the whole Zealandia continent, as explained so well in the excellent YouTube video “Greywacke Bedrock – The Backbone of New Zealand”. Material was eroded from the ancient super-continent, Gondwana, to be deposited in the sea along its eastern coast, forming the basis for Zealandia and New Zealand. Undersea avalanches and strong turbidity currents meant a mix of grain sizes can be found in greywacke (Wikipedia). The rocks were deformed by a range of immense forces along the plate boundary that now runs the length of New Zealand, opening up room for mineral veins.

From YouTube video on origin of New Zealand’s greywacke. http://www.youtube.com/watch?v=z13tAcSYVdo

From an excellent powerpoint slide show on greywacke. Source: http://www.slideshare.net/MOHITRKSINGH/wacke-graywacke

From an excellent powerpoint slide show on greywacke. Source: http://www.slideshare.net/MOHITRKSINGH/wacke-graywacke

An assortment of angular grains in a fine-grained clay – greywacke under a microscope. Source: https://teara.govt.nz/en/photograph/9065/greywacke-under-the-microscope

Both greywacke and argillite are sedimentary rocks, with greywacke being a sandstone and argillite being a mudstone. A sandstone has grains that are visible to the eye while the tiny grains making up a mudstone are not visible without magnification (see University of Auckland on grain size in sedimentary rocks). The grains in sandstones and mudstones, and the fragments in breccia, are called “clasts”, meaning fragments or particles broken off other rocks by physical weathering. According to the University of Auckland, greywacke is “a variety of argillaceous sandstone that is highly indurated and poorly sorted”. “Argillaceous” means containing a significant amount of very fine silt and/or clay – Hamish Campbell refers to it as a “muddy sandstone”. “Highly indurated” means hardened by heat, pressure or by the addition of a cementing ingredient like silt or clay, a bit more than with most sedimentary rocks. “Poorly sorted” means that its angular grains of quartz, feldspar and other minerals present have a range of sizes. An excellent summary of the characteristics of greywacke and its formation can be found in this slide show. The University of Auckland also notes that because greywacke has been subjected to significant amounts of tectonic movement over a long period of time, it is often extremely deformed, fractured, and veined with zeolite or quartz. Stones W82 to W86 above are good examples of greywacke with white veins.

In an excellent article on greywacke in “New Zealand Geographic” in 1999, Hamish Campbell points out how important the rock is to New Zealand. “Greywacke has itself been eroded to form the soft and much younger papa sandstones and mudstones of Taranaki, Wanganui, Manawatu and elsewhere. In the South Island, all the central mountains are greywacke, and the Canterbury Plains are just a sheet of greywacke rubble sluiced out of the Southern Alps. Most of Marlborough, Canterbury and Otago are greywacke. Even the schists of Otago are derived from greywacke—it has just been more deeply buried, and transformed into schist. And even that is not the end of the stuff. Under much of our vast continental shelf lies more greywacke. Out to the Chathams, south to the Campbell Plateau, it is probably all greywacke.” (Also, see this Post for an interesting explanation for why greywacke-derived soils in New Zealand are excellent for growing grapes.)

Argillite is a hardened mudstone, consisting of much smaller grains than greywacke and feeling much smoother. In New Zealand, greywacke and argillite often exist side by side in layered bands or strata. And, like greywacke, argillite has been deformed, fractured and veined because of significant amounts of tectonic movement over a long period of time (see University of Auckland). Stone W88 above is a good example of fractured argillite. Below left is a photo of pale grey greywacke rock lying above a band of dark grey argillite – in the greywacke there are a few, mostly thick veins of probably quartz, maybe calcite, while in the argillite, the white veins are thinner and more dispersed (from a geothermal website).

Greywacke = pale grey rock; Argillite = darker grey. Location is Whakatane Heads. Source: http://www.geothermalnextgeneration.com/updates/exploring-deep-basement-rocks-from-the-surface

Two specimens of greywacke in Riverton Aparima Museum, showing different hues.

Green argillite from Riverton Aparima. Source: http://www.researchgate.net/publication/275213606_The_use_of_Southland_Argillite_in_New_Zealand_Prehistory_distribution_chronology_and_form?_tp=eyJjb250ZXh0Ijp7ImZpcnN0UGFnZSI6Il9kaXJlY3QiLCJwYWdlIjoicHVibGljYXRpb24ifX0

Argillite rock on display outside Riverton Aparima Museum. Source: http://www.stuff.co.nz/southland-times/news/4554948/Rare-Riverton-rocks-attract-big-interest

For more on argillite, see Wikipedia and Terraindex.

7 – STONES WITH OPAQUE WHITE BANDS

I commented above that bands are layers that are an integral part of the original stone, such as a layer of differently coloured sediment in a sedimentary stone. I was unsure whether the white parts of Stones W88, W89 and W104 were bands or veins. From my observations on Gemstone Beach, there are far fewer stones with white bands than with white veins. Here are three candidates – the first one (Stone W114) I am sure of, the other two I am not so sure – I don’t know enough about veins and their infills to have any certainty.

Stone W114 is called a “banded argillite”. This is a good clue that it’s white lines are bands rather than veins. Grey and brown are the most common colours of the bands but in this case some white is apparent. Many of the banded argillites I have seen on Gemstone Beach seem to differ from other argillites there – they seem to have been subjected to higher temperatures, appearing more fused or melted, with a “pottery glaze” look.

Stone W114, banded argillite with thin white bands.

Other banded argillite stones from Gemstone Beach and nearby:

Banded argillite in Riverton Aparaima Museum Poster of Gemstone Beach stones.

Riverton Aparima Museum display.

Grey banded argillite from vicinity of Gemstone Beach. Found in March 2022. https://tumblestoneblog.wordpress.com/2023/03/31/southern-sojourn-202333-four-hour-fossick-gemstone-beach-te-waewae-bay-friday-31-march/

Brown banded argillite from vicinity of Gemstone Beach. Found in March 2022. https://tumblestoneblog.wordpress.com/2023/03/20/southern-sojourn-202326-delightful-discoveries-desperate-de-pants-ing-and-dramatic-drenchings-on-gemstone-beach-sunday-19-march/

Stone W115 (below) appears to me to be banded. It is a type of quartz with a well-defined white layer through it.

Stone W115, white-banded quartz?

The white line through Stone W116 seems to me upon careful scrutiny to perhaps be a concentration of the white material (a band) found scattered throughout the stone.

Stone W115, white-banded igneous stone?

It can sometimes be difficult to decide whether a white line in a stone is a vein or band. But it is always worthwhile looking closely to try to see what is going on in a stone.

The next Post in this Series looks at Gemstone Beach stones with opaque white “patches”.

DISCLAIMER: Over the past six years I have visited Gemstone Beach more than 150 times, also walking further along the Te Waewae Bay coast. But I am not a geologist – I am an amateur beach stone collector and polisher. I have done some reading and research about different types of stones, but my knowledge is limited and open to correction. Some of the photos used in these Posts were taken at Gemstone Beach in April 2023; some come from my fossicking trips there over the past three or four years; and a few were taken after I looked through my “finds” in my stone shed at home. All the stones are “rough”, not polished. The coverage of stones is not comprehensive and is biased by my own interests and what catches my attention. The photos are not perfect, often having some reflections in them. But I hope these Posts prove useful to the “passing motorist” and others who find themselves on this interesting beach. 

Go to GEMSTONE BEACH AND ITS STONES: AN INTRODUCTION FOR THE PASSING MOTORIST – PART ONE, LOCATION AND CARPARK

Return to GEMSTONE BEACH

HOME – FOSSICKING BEACHES – BEACH STONES – TUMBLE-POLISHING

Amygdaloidal stone, Gemstone Beach.

Igneous stone, Gemstone Beach.

Igneous stone, Gemstone Beach.

Gemstone Beach, in front of the carpark, on a sunny day.

This Series of Posts provides an introduction to Gemstone Beach (Orepuki, Southland, New Zealand) and a basic guide to many of the stones commonly found on that beach. Previous Posts = Part One: Location and Carpark; Part Two: Main Features of the Beach; Part Three: Sources of Information & What is a Gemstone; Part Four: Brief Introduction to Geological Terms for Stones; Part Five: Translucent Stones; Part Six-A: Stones that are Predominantly White.

The previous Post looked at three types of stones, or parts of stones, that can be found on Gemstone Beach that are white: 1 – White Milky Quartz Stones; 2 – White Hydrogrossular Garnets; and 3 – White in Other Coloured Hydrogrossular Garnets. This Post looks at two other groupings of white stones: 4 – Stones with Opaque White Spots, and 5 – Stones with Opaque White Crystals. The next Post looks at stones with opaque white veins and bands, with the following Post looking at stones with opaque white “patches”. There could be other types of white stones on Gemstone Beach but these are the ones I am currently aware of that are most likely to be found.

4 – STONES WITH OPAQUE WHITE SPOTS

Some stones on Gemstone Beach are black (or maybe red, less often green) with white or light-coloured spots. These are usually either amygdaloidal stones (what the Riverton Aparima Museum poster describes as volcanic stones with “filled bubbles”) or they are volcanic stones within which crystals have formed as the rock has cooled (next section). It is not always easy to tell which are which. But many of these stones have a very interesting appearance and some are very attractive.

THE WHITE “SPOTS” OF AMYGDALOIDAL STONES

The following four stones with white spots are good examples of amygdaloidal stones. In general, the white “spots” are circular or deformed circles, with a well-defined boundary.

Stone W30, volcanic amygdaloidal stone.

Stone W31, volcanic amygdaloidal stone.

Amygdaloidal stone, Gemstone Beach.

Stone W32, volcanic amygdaloidal stone.

Stone W33, volcanic amygdaloidal stone.

How are these amygdaloidal stones formed? Molten magma often contains dissolved gas which can form bubbles in the rock as the pressure is released on eruption. These bubbles can get trapped in the solidified rock, forming tiny holes (called “vesicles”). These holes then fill with mineral-rich fluids which leave behind deposits of minerals such as quartz, chalcedony (agate), calcite and zeolites (zeolites are a group of minerals with a crystalline structure made up of silicon, aluminum, and oxygen). The resultant “spots” are called “amygdales” (also called “amygdules”), a term that comes from the Latin and Greek words for almond, reflecting the almond-shape of many such in-filled vesicles. However, many amygdales are round and others can be irregular shapes, as demonstrated by the Gemstone Beach examples in this Post and the six specimens on display at the Riverton Aparima Museum (see photo below, far left). The three photos below to the right are of different kinds of amygdaloidal basalt.

Amygdaloidal stones in Riverton Aparima Museum.

Amygdaloidal stones in Riverton Aparima Museum poster.

Amygdaloidal basalt from Isle of Skye, Scotland. Source: http://www.therockgallery.co.uk/amygdaloidal-basalt—isle-of-skye-3373-p.asp

Amygdaloidal basalt, infilled with chalcedony and chlorite (black infill), Michigan USA. Source: http://www.mindat.org/photo-1137645.html

Amygdaloidal basalt, inflilled with chalcedony and pumpellyite (the dark green centres), Michigan USA. Source: http://www.mindat.org/photo-1137644.html

“Amygdaloidal” is a term that refers to the way the stone has formed rather than the material it consists of. By far the most common volcanic amygdaloidal rock is basalt, though andesite, for example, can also be amygdaloidal. For more on amygdaloidal rocks, see Alex Strekeisen, Wikipedia, Ontario Beneath Our Feet, and University of Oxford Earth Sciences.

You can sometimes find quite attractive red amygdaloidal stones on Gemstone Beach with a range of amygdale shapes and colours, including white. While basalt is often a dark black or gray colour, red is also a not uncommon colour. Here are five examples which well illustrate the variations – note the irregular amygdale shapes in Stone W36 and the different colours in Stones W37 and W38:

Stone W34, volcanic amygdaloidal stone.

Stone W35, volcanic amygdaloidal stone.

Stone W36, volcanic amygdaloidal stone.

Stone W37, volcanic amygdaloidal stone.

Stone W38, volcanic amygdaloidal stone.

Finally, four more examples of amygdaloidal stones found on Gemstone Beach, a couple of which have a noticeably green host rock. The book “A Photographic Guide to Rocks & Minerals of New Zealand” notes on page 58: “Geologically old basalts (older than 100 million years or so) have recrystallised and can be a dark green colour because they contain the minerals chlorite and epidote”. Also note that the colour of the amygdales in Stone W39 is not a bright white, almost verging on the translucent maybe.

Stone W39, volcanic amygdaloidal stone.

Stone W40, volcanic amygdaloidal stone.

Stone W41, volcanic amygdaloidal stone.

Stone W42, volcanic amygdaloidal stone.

5 – STONES WITH OPAQUE WHITE CRYSTALS

Most of the stones with opaque white crystals on Gemstone Beach are igneous in origin, as will be seen. To deal first with white and black stones made up of tiny crystals. A number of variations of these can be found on Gemstone Beach. The size of the crystals, their shape, and the ratio of white to black can all vary quite a bit, as illustrated by these seven examples which at first glance look nearly identical:

Stone W43, tiny white and black crystals.

Stone W44, tiny white and black crystals.

Stone W45, tiny white and black crystals.

Stone W46, tiny white and black crystals.

Stone W47, tiny white and black crystals.

Igneous stone, Gemstone Beach.

Stone W48, tiny white and black crystals.

Stone W49, tiny white and black crystals.

There is an amazing variety of white crystals in these stones. Some of the white crystals are quite small, some larger. They have different shapes, some being square or rectangular, some being elongated or stretched out. Some having an indistinct shape but many are individually apparent, while others appear clumped together.

These stones are all likely to be volcanic or plutonic stones within which crystals have formed as the rock has cooled (Part 4 in this Series briefly defines volcanic and plutonic as two types of igneous rocks, rocks formed by the cooling of molten material). I find it difficult to identify the type of rock each stone comes from, and the identity of the white crystals varies from quartz to feldspar, among others, but the process that produces the white and black crystal mix is clear (and will be described more fully below, after Stone W81). To the north and west of Gemstone Beach are geological features in Fiordland with origins in molten rocks. Due to glaciation and other forms of erosion, stones from these features have eventually made their way down to the Waiau River system and out to sea and then onto Gemstone Beach.

In the next seven white and black stones from Gemstone Beach, the white crystals are larger:

Stone W50, black with small white crystals.

Stone W51, black with small white crystals.

Stone W52, black with small white crystals.

Stone W53, black with small white crystals.

Stone W54, black with small white crystals.

Stone W55, black with small white crystals.

Stone W56, black with small white crystals.

Sometimes with this type of white and black stone, the component of white can be tiny, as with Stones W57 and W58:

Stone W57, black stone with tiny white crystals.

Stone W58, black stone with scattered tiny white crystals.

There is a wide variety of types of this dark-coloured stone with white crystals – it pays to look closely and carefully to check out the characteristics of the crystals. Three further examples of the variety of the nature and shape of the white crystals:

Stone W59, white crystals of different sizes.

Stone W60, white crytsals plus some larger black crystals, along with a thin green-hued vein.

Stone W61, slightly less well-defined white crystals.

Sometimes the white component dominates a stone, with the white crystals seeming to clump together to make larger groupings:

Stone W62, clumps of white crystals.

Igneous stone, Gemstone Beach.

Stone W63, clumps of opaque white crystals.

Sometimes a dash of colour can be found in a stone of opaque white crystals, due to the presence of a mineral, such as the reddish-brown iron oxide in Stone W64:

Stone W64, white crystals and iron oxide patches.

Apart from Stone W64, so far the non-white component of these stones has been black or dark gray, with Stone W62 having the palest non-white matrix. But opaque white crystals can also be found in stones of other colours, such as these two green examples:

Stone W65, green-coloured stone containing some white crystals.

Stone W66, green-coloured stone containing some tiny white crystals.

The green in stones on Gemstone Beach is often due to the presence of the mineral called epidote, although other minerals give rise to green as well.

Two examples of reddish-purple stones from Gemstone Beach that contain white crystals:

Stone W67, reddish-purple stone with white crystals.

Stone W68, reddish-purple stone with white crystals.

There is a variety of pink stones on Gemstone Beach, the pink caused by the presence of the mineral thulite, that often have white crystals showing within them. Some of these stones are even purple in colour, as with Stone W71. Thulite is often associated with quartz and, unlike most of the other stones with white crystals, is a metamorphic stone rather than an igneous one.

Stone W69, pink thulite stone with white crystals.

Stone W70, pink thulite stone with white crystals.

Stone W71, purple thulite stone with white crystals.

Five examples of brown stones with white crystals, the first four likely to be rhyolite:

Stone W72, brown stone (rhyolite?) with white crystals.

Stone W73, brown rhyolite stone with white crystals.

Stone W74, brown rhyolite stone with white crystals.

Stone W75, brown rhyolite stone with white crystals.

Stone W76, brown stone with white crystals.

There are also a variety of stones with white crystals on Gemstone Beach that are granite. Some are quite light coloured (known as “pale granite”) while others (known as “pink granite”) have a pink-orange feldspar in them:

Stone W77, pale coloured granite.

Stone W78, pale coloured granite.

Stone W79, “pink” granite.

Stone W80, darker “pink” granite.

Finally, to re-emphasise the great variation of stones on Gemstone Beach, a light coloured stone with a handful of opaque white crystals, or clumps of crystals:

Stone W81, light coloured stone with a handful of white crystals (clumps?).

What explains the different sizes and shapes of most if not all of the white crystals in Stones W43 to W81? The answer lies in their origin in molten rock. It all depends on how quickly the molten rock has cooled and hardened, and what minerals present in the molten rock make up the crystals. A “volcanic” rock cools on the earth’s surface and, because it has solidified quickly, the crystals have not had time to grow very large. But for a “plutonic” rock, the molten rock has cooled much more slowly underground, giving the crystals time to grow larger, sometimes as large as fingernails. Sometimes an igneous rock has both fine-grained and larger crystals – this is called a “porphyry”, referring to the “texture” of the rock. A porphyry has well-formed crystals visible to the naked eye (called “phenocrysts”), set in a very fine grained matrix (see the two photos below right). This happens when magma that has been slowly cooling and crystallising within the Earth’s crust is suddenly erupted at the surface, causing the remaining uncrystallised magma to cool rapidly (see “Textures of Igneous Rocks” in University of Auckland Geology). So a porphyry is intermediate between quickly solidifying fine-grained rocks and the slowly solidifying rocks with uniform larger crystals. Stones W54, W55 and W56 above are good examples of a porphyry. Note that “porphyry” is a term describing the relative crystal sizes in rocks, it’s not a rock type like basalt, rhyolite and granite.

Examples of volcanic stones from a beach close to Gemstone Point. From a display at the Riverton Aparima Museum.

Close-up of volcanic rocks, Riverton Aparima Museum.

Porphyry stones in Riverton Aparima Museum poster.

Porphyry specimens. Riverton Aparima Museum.

Porphyry specimen. Riverton Aparima Museum.

There are a number of well-known shapes, or “habits”, of crystals, although the exact number is not agreed upon, and different terms are sometimes used for the same shape. The Mineralogical Society of America provides the following examples of shapes or habits (among others): blocky or equant (having equal sides), tabular (which can be thin or thick), prismatic, bladed (like grass or a knife), acicular (needle-like), and filiform or capillary (like hair or thread). There are also terms for different kinds of groupings of crystals, like drusy, radiating, dendritic and reticulated. See also Dexter Perkins and Geologyin.com for an introduction to habits. However, crystals in rocks tend not to grow freely in their typical shape, being crowded and squeezed by other crystals and material, or the conditions for their growth may have been inadequate or too short. It is therefore often very difficult to identify a rock type based on the crystal shapes in a stone, or the sizes of the crystals.

Despite these problems, it is worthwhile to consider some typical igneous rock types which may relate to our stones. Igneous rocks are categorised according to their composition and grain size, more than the type of crystals in them (see diagram below, at far left in next set of photos). For example, GABBRO is a plutonic rock consisting of about 50% to 90% of the dark minerals augite, olivine and hornblende. The pale mineral in gabbro is plagioclase feldspar. As shown in the diagram, gabbro does not contain any quartz. Gabbro has the same mineral composition as the volcanic rock BASALT but the grain size of the two rock types differs due to their different rates of cooling. The book “A Photographic Guide to Rocks & Minerals of New Zealand” notes on page 73 that gabbro can be found between Colac Bay and Pahia, a handful of kilometres away from Gemstone Beach. The Riverton Aparima Museum has a specimen of gabbro from Monkey Island (see photo below, centre), which is on the coast of TeWaewae Bay, just two kilometres south of Gemstone Beach.

Mineral composition of igneous rocks. Source: https://rocksminerals.flexiblelearning.auckland.ac.nz/rocks/igneous.html

On display at Riverton Aparima Museum.

Source: https://www.thoughtco.com/igneous-rock-types-4122909

Diorite specimens, Riverton Aparima Museum.

DIORITE is a plutonic rock that is generally a little lighter in colour than gabbro, consisting of 25% to 50% of dark minerals (see photos above, right, which also illustrates the variation in diorite). A small amount of quartz may be found in diorite (as shown in the diagram above, far left). Fine-grained gabbro and diorite is sometimes called DOLERITE (or diabase), which tends to occur in dikes and sills (sheets of rock that are formed in a fracture of a pre-existing rock body when magma is forced through). The specimens of dolerite stones in the Riverton Aparima Museum, two of which are from Gemstone Beach, again show quite a variation in appearance (see photos below).

Dolerite (or diabase). Source: https://geologyscience.com/rocks/igneous-rocks/intrusive-igneous-rocks/diabase-or-dolerite/

Specimens of dolerite, Riverton Aparima Museum.

Riverton Aparima Museum.

Close-up of dolerite stones, Riverton Aparima Museum.

Stones W43 to W61 above all have white and black crystals. The ones with the smaller crystals are likely to be plutonic and the ones with larger crystals could be volcanic. However, I am unable to identify any particular stone as being gabbro or diorite, for example, or as GRANODIORITE, which comes between granite and diorite (it has more quartz than diorite). I don’t have the knowledge to do so. But these stones all started as molten rock and then their crystals formed as the rock hardened. It’s amazing to see how diverse is the mix of crystals, along with their shape and their arrangement.

Another plutonic rock mentioned in the diagram above (of mineral composition in igneous rocks) is GRANITE. It is the lightest in colour of the plutonic rocks, consisting of only 5% to 25% of dark minerals. The dark mineral is usually black mica biotite, sometimes hornblende. The pale minerals include white plagioclase feldspar, pink orthoclase feldspar and a pale gray quartz, with a white muscovite mica also possible. Granite has more quartz in it than the other rocks we have been considering in this part of this Post. The Riverton Aparima Museum has three specimens of granite (see photo below, second from left) showing how its colour can vary considerably. It also has on display bowls of pale and pink granite. The book “A Photographic Guide to Rocks & Minerals of New Zealand” notes on page 75 that granite is exposed along the coast between Orepuki and Colac Bay. More information about granite in general can be found here.

Source: https://rocksminerals.flexiblelearning.auckland.ac.nz/rocks/granite.html

Riverton Aparima Museum.

Riverton Aparima Museum.

Riverton Aparima Museum.

As noted above in relation to Stones W77 to W80, RHYOLITE stones can be found on Gemstone Beach. Rhyolite has the same chemical composition as granite but is a volcanic version of it.

Note: An excellent introduction to Fiordland’s geology, the most likely source of stones on Gemstone Beach, is the ten minute YouTube video “Fire, Ice, and Tremors – Episode 1: The Geologic History of Fiordland National Park”. Parts of this Post have drawn on Jocelyn Thornton’s (1985) book, “The Field Guide to New Zealand Geology”.

The next Post in this Series looks at a further two groupings of white stones that can be found on Gemstone Beach, stones with opaque white veins and opaque white bands. 

DISCLAIMER: Over the past six years I have visited Gemstone Beach more than 150 times, also walking further along the Te Waewae Bay coast. But I am not a geologist – I am an amateur beach stone collector and polisher. I have done some reading and research about different types of stones, but my knowledge is limited and open to correction. Some of the photos used in these Posts were taken at Gemstone Beach in April 2023; some come from my fossicking trips there over the past three or four years; and a few were taken after I looked through my “finds” in my stone shed at home. All the stones are “rough”, not polished. The coverage of stones is not comprehensive and is biased by my own interests and what catches my attention. The photos are not perfect, often having some reflections in them. But I hope these Posts prove useful to the “passing motorist” and others who find themselves on this interesting beach. 

Go to GEMSTONE BEACH AND ITS STONES: AN INTRODUCTION FOR THE PASSING MOTORIST – PART ONE, LOCATION AND CARPARK

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White milky quartz stone, Gemstone Beach.

White quartz stone with tiny reddish dots, Gemstone Beach.

Opaque white hydrogrossular garnet, Gemstone Beach.

Gemstone Beach, in front of the carpark, on a sunny day.

This Series of Posts provides an introduction to Gemstone Beach (Orepuki, Southland, New Zealand) and a basic guide to many of the stones commonly found on that beach. Previous Posts = Part One: Location and Carpark; Part Two: Main Features of the Beach; Part Three: Sources of Information & What is a Gemstone; Part Four: Brief Introduction to Geological Terms for Stones; Part Five: Translucent Stones.

DISCLAIMER: Over the past six years I have visited Gemstone Beach more than 150 times, also walking further along the Te Waewae Bay coast. But I am not a geologist – I am an amateur beach stone collector and polisher. I have done some reading and research about different types of stones, but my knowledge is limited and open to correction. Some of the photos used in these Posts were taken at Gemstone Beach in April 2023; some come from my fossicking trips there over the past three or four years; and a few were taken after I looked through my “finds” in my stone shed at home. All the stones are “rough”, not polished. The coverage of stones is not comprehensive and is biased by my own interests and what catches my attention. The photos are not perfect, often having some reflections in them. But I hope these Posts prove useful to the “passing motorist” and others who find themselves on this interesting beach.

I have organised my presentation of the stones of Gemstone Beach by COLOUR. The main advantage of this is that colour is probably the most obvious characteristic of a stone. However, keep in mind that colour perception can vary at least a little from person to person. The angle of your phone or computer screen, and any “eye comfort” filter you have on your phone, can also affect the hue of the colour you see. Remember, look at the stones when they are wet to see their colours clearly. Also, stones can have a lot of detail in them which can be missed at first glance. Look at a stone up close, carefully, turning it over to view all sides. Sometimes, taking a photo with your phone then zooming into the image can be quite revealing.

WHITE STONES ON GEMSTONE BEACH

White stones are often the first you see on a beach – they stand out among the darker coloured stones, especially when wet but also when dry.

Gemstone Beach stones, dry.

Gemstone Beach stones, wet.

Gemstone Beach stones, wet.

Upon closer inspection, there seem to be a variety of shades of white, from almost clear (translucent) to dense and opaque. Some stones are completely white, other stones contain white spots or crystals, others seem to have white veins or patches. This Post looks at three types of stones, or parts of stones, that can be found on Gemstone Beach that are white: 1 – White Milky Quartz Stones; 2 – White Hydrogrossular Garnets; and 3 – White in Other Coloured Hydrogrossular Garnets. The next Post looks at stones with opaque white spots and crystals, and the Post after that considers stones with opaque white veins and patches. There could be other types of white stones on Gemstone Beach but these are the ones I am currently aware of that are most likely to be found.

1 – WHITE MILKY QUARTZ STONES

Below are three white quartz stones, W1, W2 and W3 (“W” stands for White) found on Gemstone Beach. They are opaque (light doesn’t shine through them) and are nearly purely white. These are sometimes referred to as cloudy or milky quartz, and there seems to be some very minor variations within each in terms of their opaqueness. As with many such beach quartz stones, these are spherical or egg-shaped, and quite smooth.

Stone W1, white milky quartz.

Stone W2, white milky quartz.

Stone W3, white milky quartz.

As I noted when looking at translucent quartz stones, quartz is a form of silica and is one of the most common minerals on Earth. It is a component of a wide variety of sedimentary, metamorphic and igneous rocks (these terms are explained in Part Four of this Series). The white veins and bands seen in stones are usually composed of quartz. Its purest variety is a clear colourless form known as rock crystal. A violet coloured variety is amethyst and a pink form is rose quartz – and there are many more variations. Quartz is usually viewed as an igneous rock that crystallizes from magma or precipitates around hydrothermal vents. As Wikipedia notes: “Milky quartz is the most common variety of crystalline quartz. The white color is caused by minute fluid inclusions of gas, liquid, or both, trapped during crystal formation.” For more on quartz as a mineral, see “Quartz – Te Ara Encyclopedia of New Zealand”, “Quartz” in University of Auckland Geology website, “Quartz” in Mindat.org, and “Quartz” (page 10) in Thornton’s “Gemstones”.

Some white milky quartz stones contain small specks (Stones W4 and W5 below) or stains or patches of another mineral, often iron oxide. For example, the rusty iron oxide stains on the top of Stone W6 (below) are relatively common.

Stone W4, white milky quartz stone with tiny black inclusions.

Stone W5, white milky quartz stone with tiny reddish brown inclusions.

Stone W6, white milky quartz stone with rusty iron oxide stains at top.

Sometimes white milky quartz stones can vary noticeably in material, such as those with patches of variable opaqueness and translucency, as with Stones W7 to W9 below (Note: Stone W9 is the same stone as Stone T41 in Translucent Stones):

Stone W7, white milky quartz with patches of variable opaqueness.

Stone W8, white milky quartz with patches of variable opaqueness.

Stone W9, white milky quartz with some translucent areas.

Other variations of milky quartz exist – every white stone is practically unique.

2 – WHITE HYDROGROSSULAR GARNETS

Some white stones on Gemstone Beach kind of look like white milky quartz but have a different feel and a slightly different appearance. They are hydrogrossular garnet stones, with Stones W10, W11 and W12 (below) being good examples:

Stone W10, white hydrogrossular garnet.

Stone W11, white hydrogrossular garnet.

Stone W12, white hydrogrossular garnet.

Note that Stone W12 (above) has some thin translucent-looking veins as well as a couple of bright white opaque veins. Stones W10 and W11 lack such veins. Often small white pieces of such stones, the size of a fingernail, sit shining brightly on the beach. Gemstone Beach is well known for hydrogrossular garnets and is probably the beach on which they can be most easily found in New Zealand. Despite that, they don’t always show up. I usually find one or two each visit, and often find maybe a handful more by walking a few hundred metres further northwards along the Te Waewae Bay coast. However, some visits do not yield any specimens.

Hydrogrossular garnets often feel waxy, and they have a slightly duller look than white milky quartz. Some exceptions exist and will be noted below and in other Posts. When wet, water tends to “bead off” the waxy surface of these stones, forming beads or droplets that roll off. The stones that shine most bright on the beach are white milky quartz and white hydrogrossular garnets.

Hydrogrossular stones come from a metamorphic rock called rodingite which has other minerals mixed in as well. Sometimes a tiny bit of other material is incorporated into the white opaque hydrogrossular garnet stones. Black or gray is common (as with Stones W13 and W14) as is yellow (Stones W16 and W17 are good examples). Also note that W16 is an example of a denser white form of hydrogrossular garnet, while the lower part of Stone W17 appears to be almost colourless.

Stone W13, white hydrogrossular garnet.

Stone W14, white hydrogrossular garnet.

Stone W15, white hydrogrossular garnet.

Stone W16, white hydrogrossular garnet.

Stone W17, partly white hydrogrossular garnet.

Some white hydrogrossular garnets have quite a variable character, with patches of different shades of white, some tiny areas or veins also looking translucent. Stones W18 to W21 are examples:

Stone W18, variable white hydrogrossular garnet.

Stone W19, variable white hydrogrossular garnet.

Stone W20, variable white hydrogrossular garnet.

Stone W21, variable white hydrogrossular garnet.

There is another kind of white hydrogrossular garnet on Gemstone Beach that is very opaque and which often does not have a waxy feel. It is one of the most common variations to be found there. In my TumbleStone Two Post on the seven main types of hydrogrossular garnets, they are listed as the fifth type, “white stones with dark intrusions”. In Thornton’s entry on “Garnet” on page 9 of her book on “Gemstones”, at the top left of the photo of stones and numbered “1” is a photo of such a stone. Thornton refers to it as “a stone from the beach at Orepuki, showing a dark crystal of diopside in the garnet.” The diopside has a black or dark gray or silver appearance. In Stone W14 (above), it might be diopside that is lurking just under the surface at the bottom of the stone, and Stone W21 (immediately above) shows such a dark silvery crystal. Below are three examples of the dense white hydrogrossular garnets with diopside, Stone W24 having a number of smaller black inclusions:

Stone W22, white hydrogrossular garnet with diopside.

Stone W23, white hydrogrossular garnet with diopside.

Stone W24, white hydrogrossular garnet with diopside.

Stones W25 and W26 are maybe also versions of this, with much smaller diopside crystals in them – again, these stones often don’t have a waxy feel, but I have learned they have hydrogrossular garnet in them by talking to other rockhounds in person and on the internet:

Stone W25, white hydrogrossular garnet with small diopside crystals?

Stone W26, white hydrogrossular garnet with small diopside crystals?

Sometimes the white opaque variety of hydrogrossular garnets has a pink blush in them, most likely due to thulite being present. Examples will be provided in the Post on “Pink Stones” (not yet available).

3 – WHITE IN OTHER-COLOURED HYDROGROSSULAR GARNETS

Hydrogrossular garnets come in a range of colours. For example, in her book “The New Zealand Rockhound” (1981), Natalie Fernandez notes on page 50: “Hydrogrossular garnet is a massive form of calcium garnet…Colour: A wide range, patchy. Pale green, greyish, yellow, white, brown. Occasionally shades of orange, darker green, even blue and pink.” Some of the coloured hydrogrossulars also contain some white – see three examples below. These three stones have a waxy feel that help to identify them as hydrogrossular garnets.

Stone W27, coloured hydrogrossular garnet with white.

Stone W28, coloured hydrogrossular garnet with white.

Stone W29, coloured hydrogrossular garnet with white.

Note that, in general, hydrogrossular garnets are not common on Gemstone Beach but can occasionally be found there. We will come across hydrogrossular garnets again in Posts on other colours.

The next Post in this Series looks at two further groupings of white stones that can be found on Gemstone Beach, stones with opaque white spots and stones with opaque white crystals.

Go to GEMSTONE BEACH AND ITS STONES: AN INTRODUCTION FOR THE PASSING MOTORIST – PART ONE, LOCATION AND CARPARK

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Translucent quartz stone, Gemstone Beach.

Translucent hydrogrossular garnet, Gemstone Beach.

Translucent veins in quartzite, Gemstone Beach.

Gemstone Beach, in front of the carpark, on a sunny day.

This Series of Posts provides an introduction to Gemstone Beach (Orepuki, Southland, New Zealand) and a basic guide to many of the stones commonly found on that beach. Part One presented the location and geographical context for Gemstone Beach, and described its carpark and local beach warnings. Part Two set out the main features of Gemstone Beach and noted different beach conditions. Part Three provided a general introduction to the stones of the beach, referring to some already existing sources of information, and discussed the meaning of “gemstone”.  Part Four provided some brief definitions of important geological terms useful in later Posts. This Post is the first of a number on different stones listed by colour.

DISCLAIMER: Over the past six years I have visited Gemstone Beach more than 150 times, also walking further along the Te Waewae Bay coast. But I am not a geologist – I am an amateur beach stone collector and polisher. I have done some reading and research about different types of stones, but my knowledge is limited and often open to correction. There is an amazing diversity of stones on that beach, each unique in some way. In these Posts, I am sharing what I know – it is not expert knowledge and it is not comprehensive. Some of the photos used in these Posts were taken at Gemstone Beach in April 2023; some come from my fossicking trips there over the past three or four years; and a few were taken after I looked through my “finds” in my stone shed at home. All the stones are “rough”, not polished. I have also included photos of stones that I have found up to about 400 metres from Gemstone Beach, along the coast of Te Waewae Bay – the same types of stones can be found for many kilometres along this coast.

After some thought, I have decided to organise my presentation of the stones of Gemstone Beach by COLOUR. The main advantage of this is that colour is probably the most obvious characteristic of a stone. However, colour perception can vary from person to person, and I am aware that I don’t always see subtleties of colour the same as others. Keeping this in mind, I will do the best I can. Also note that the angle of your phone or computer screen, and any “eye comfort” filter you have on your phone, will also affect the hue of the colour you see.

Remember, look at the stones when they are wet to see their colours clearly. Also, stones can have a lot of detail in them which can be missed at first glance. Look at a stone up close, carefully, turning it over to view all sides. Sometimes, taking a photo with your phone then zooming into the image can be quite revealing.

A NOTE ON THE PHOTOS OF STONES BELOW

Each stone is numbered – “T1” means Translucent stone #1. In all cases, the first photo is of the stone in my hand, giving an idea of its size and what it looks like from a slight distance. The second photo is a close-up one, revealing more details. The third photo is usually the stone held up to the sky, and a fourth photo is sometimes provided of the stone with a torch behind it – the third and fourth photos demonstrate its translucent character.

TRANSLUCENT STONES

Stone T1, translucent quartz.

Light shines through all or part of a translucent stone.

With a torch behind the stone.

Occasionally, a “translucent” stone can be found on Gemstone Beach. As with Stone T1 (see photos above), a quartz stone with some mineral inclusions, when this type of stone is held up to the sky or when a torch is placed behind it, some (maybe only a little) light passes through it. It’s like looking through dull or fuzzy glass. “Translucent” is one of the three main ways of classifying how light passes through a stone. The first type is “transparent”, meaning light passes through the stone easily, as through clear glass or a clear quartz crystal; “translucent” means only limited light is able to pass through the stone, so that an object held behind it would look fuzzy; and the third category is “opaque”, meaning light does not pass through the stone at all (most stones are opaque). An interesting web page on the three categories provides the following useful illustrations:

Source: https://www.gemstones.com/articles/gemstone-transparency

Source: https://www.gemstones.com/articles/gemstone-transparency

Source: https://www.gemstones.com/articles/gemstone-transparency

Make sure if you lift up a stone to see if light passes through it that you don’t end up looking directly at the sun! Using the torch on your phone can be a safer option.

This Post looks at four types of stones, or parts of stones, that can be found on Gemstone Beach that are translucent. Three of them are relatively rare while the fourth type is more common. There could be other types of translucent stones but these are the four I am currently aware of.

1 – Translucent Quartz Stones

The following are seven more quartz stones that are translucent to varying degrees. You can mainly see this when you hold the stones up to a light source. When doing so, you will also notice any other material in the stone that blocks the light – often this will be a mineral like iron oxide. Sometimes the mineral will be in an obvious opaque patch as in Stone T2, or in a tracery of fine threads only visible against the light as in Stone T3, or in a more noticeable pattern even before being held up to the light as in Stone T6. Stones T7 and T8 contain tiny black specks, again a mineral inclusion in the stones. Some of the stones do not let much light through at all, though it is possible to see a little way beyond the surface, into the depth of the stone. Maybe the phrase “partly translucent” might be a more accurate term to describe these ones.

Stone T2, translucent quartz.

With a torch behind the stone.

Stone T3, translucent quartz.

With a torch behind the stone.

Stone T4, translucent quartz.

With a torch behind the stone.

Stone T5, translucent quartz.

With a torch behind the stone.

Stone T6, translucent quartz.

With a torch behind the stone.

Quartz stones are more often an opaque white, being milky in appearance (see the Post on white stones) but this translucent variety can also be found on Gemstone Beach.

Quartz is a form of silica and is one of the most common minerals on Earth. It is a component of a wide variety of sedimentary, metamorphic and igneous rocks. The white veins and bands seen in stones are usually composed of quartz. Its purest variety is a clear colourless form known as rock crystal. A violet coloured variety is amethyst and a pink form is rose quartz – there are many more variations. Quartz is usually viewed as an igneous rock that crystallizes from magma or precipitates around hydrothermal vents. The metamorphic rock that forms with a very high quartz content is called quartzite and some of the beach stones we call quartz could in fact be quartzite. For more on quartz as a mineral, see “Quartz – Te Ara Encyclopedia of New Zealand”, “Quartz” in University of Auckland Geology website, “Quartz” in Mindat.org, and “Quartz” (page 10) in Thornton’s “Gemstones”.

2 – Translucent Hydrogrossular Garnets

Some translucent stones on Gemstone Beach look initially like quartz but have a different feel and a slightly different appearance. They feel waxy, and they have a slightly duller look, although when wet they shine brightly on the beach. These are metamorphic stones with the mineral hydrogrossular garnet in them (they come from a rock called rodingite which has other material mixed in as well). Stone T9 (below) is a good example of their waxy and slightly dull character. Also, when these stones are wet, water tends to “bead off” their waxy surface, forming beads or droplets that roll off. The photos of Stones T10, T11 and T12 below show the variable translucent character of the stones. Stone T10 has some brighter white patches as well as three darker inclusions. Half of Stone T11 has a light yellow hue, probably from iron oxide. Stone T12 is translucent mainly at one end.

Stone T9, translucent hydrogrossular garnet.

Close-up of the stone’s surface.

Stone T10, translucent hydrogrossular garnet.

Stone T11, translucent hydrogrossular garnet.

Stone T12, translucent hydrogrossular garnet.

The following photos of other translucent hydrogrossular garnets from Gemstone Beach include images with a torch behind them, adding to the appreciation of the opaque areas that can also exist within these stones. Stone T13 has a tiny bead of water on it due to its waxy surface. Stone T14 has a small dark crystal in it – Thornton suggests this could be the mineral diopside (see page 9 of “Gemstones”).

Stone T13, translucent hydrogrossular garnet.

With a torch behind the stone.

Stone T14, translucent hydrogrossular garnet.

Stone T15, translucent hydrogrossular garnet.

Stone T16, translucent hydrogrossular garnet.

Stone T17, translucent hydrogrossular garnet.

Stone T18 (below) is a more glassy type of hydrogrossular garnet – this type typically has a green hue and sometimes contains small concentrated green mineral patches (chromite?). NOTE: March 2025: I have had a geologist identify this type of stone as chromite in quartz (not hydrogrossular garnet). When held up to the sky, no light seems to pass through the stone but when viewed with a torch behind it, a small degree of translucency is apparent.

Stone T18, translucent hydrogrossular garnet.

Not much translucency apparent when held up to the sky.

With a torch behind the stone.

In general, stones with hydrogrossular garnet in them are not common on Gemstone Beach but they can be found there. I usually find one or two each visit, and often find maybe a handful more by walking a few hundred metres further northwards along the Te Waewae Bay coast. However, some visits do not yield any specimens.

Hydrogrossular garnet is unlike other types of garnet, such as the more common dark red crystals used in jewelry. Chemically, hydrogrossular is a type of calcium aluminium garnet, with hydroxide partially replacing what is silica in other garnets. It forms as dense masses, not nicely shaped crystals. Hydrogrossular garnet was first identified by New Zealander Colin Hutton in 1943, from stones found in the Nelson area. Gemstone Beach and its nearby Te Waewae Bay beaches are well known for hydrogrossular garnets, which most likely come from the mountains of Fiordland, brought down to the sea by the Waiau River and its tributaries. Some rockhounds specifically go to Gemstone Beach to look for hydrogrossulars. Hydrogrossular garnet often forms as part of a rock called rodingite, which also contains the minerals plagioclase and actinolite. Rodingite starts off as a plutonic, volcanic or sedimentary rock that is then saturated with hot fluids that deposit calcium. On page 122 of the book, “A Photographic Guide to Rocks and Minerals of New Zealand”, it is noted that the Gemstone Beach rodingites formed from igneous rocks. I have written a short introduction to these stones in my TumbleStone Blog here, with a longer Post plus many photographs in my TumbleStone Two website here. There are only short entries on hydrogrossular garnet in Wikipedia and Mindat.org. There are also only brief mentions in “Te Ara Encyclopedia of New Zealand” and on page 9 in Thornton’s “Gemstones”.

3 – Mix including Translucent Quartz

Some stones that you find on Gemstone Beach look as if they consist of a mix of two or three main materials, one of which is transparent quartz. Here are three examples:

Stone T19, a mix including translucent quartz.

Stone T20, a mix including translucent quartz.

Stone T21, a mix including translucent quartz.

Stone T19 (above) seems to have small white crystals embedded in the translucent quartz while Stone T20 contains a mix of green material (maybe the mineral epidote?) and quartz. Stone T21 has a more complex mix of green with translucent as well as milky-white quartz. In these cases, the translucence provides a sense of depth, allowing you to see a little way into parts of the stone. If you hold the stone up to a light source, you are unlikely to see through the stone because of the presence of a lot of opaque material as well. This is why only three photos of each stone are being provided in this Section and the next, showing the stone as held in the hand then in more detail.

Photos of five more of this type of stone are given below, showing a range of different patterns and colours:

Stone T22, a mix including translucent quartz.