Category: Polished Stones

I met Michelle at the end of a Gemstone Beach fossick in mid-September. She had a bag of stones she had just collected and we chatted for a while. She is definitely a stone enthusiast and had visited the beach many times. Her stones are important to her. I offered to tumble polish some of her finds. It is rare for me to make such an offer – often people collect stones that are not the best for tumbling -but Michelle’s enthusiasm runs deep and I knew she would appreciate the end product. She later brought quite a few of her stones around to where I was staying so I could pick through them to select the best ones for tumble polishing in terms of size, hardness and suitability. The first batch has now finished being polished, a total of 51 stones, with a few more still in the process, needing extra tumbling.

The 51 polished stones.

The 12 stones featured in this Post.

The stones (wet) after their first tumble in 220 grit.

Gemstone Beach, I day I met M.

The stones of Gemstone Beach.

I have selected 24 of these polished stones for individual photos. This Post features 12 of them (see photo immediately above, top row, at the right) with a following Post containing the remaining 12. Stone 1 is a small thin stone, just two centimetres long. Its grey and black and small flashes of white make it quite attractive, and it has come out very smooth and very shiny. It is possibly a mudstone and is brecciated, meaning that tectonic stress has fragmented it in its history.

Stone 1.

Other side of Stone 1.

Stone 2 chose its own place in the sequence of stones – one side looks like it has the number 2 on it!

The number two on the side of Stone 2.

Other side of Stone 2.

Stone 2 is a bigger stone, three and a half centimetres long. Most of it is black, maybe of volcanic origin, with a large vein running through it. Again, the vein will have been created by tectonic stress, and there is some brecciation present (the black fragments that can be seen). The vein that opened up is filled with colourful minerals, including quartz. This stone has again tumble polished quite well, with just a small part of the second side feeling slightly rough.

Stone 3 is an igneous porphyry with a very slight blue tinge. I have found a few of these myself on Gemstone Beach and elsewhere along the Southland coast. They are an attractive stone which often polishes well. The thin dark vein through Stone 3 adds to its attractiveness.

Stone 3.

A “porphyry” has well-formed crystals visible to the naked eye (called “phenocrysts”), set in a very fine grained matrix. Porphyries develop 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. 

Stone 4 is amygdaloidal, sometimes also known as a volcanic “filled bubbles” stone. It could be basalt.

Stone 4.

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 “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 as the ones in Stone 4 are. Sometimes tumble polishing amygdaloidal stones can be a challenge as the amygdales can come loose and fall out, or the material between close amygdales can crumble. There are two tiny areas in Stone 4 where the latter has occurred but generally it has polished very well.

Stone 5 is an unusual one for Gemstone Beach, in my experience. It kind of looks like petrified mud.

Stone 5.

Other side of Stone 5.

The lighter bits look like plant material. Again, the stone has tumble polished quite well. It’s very hard, though one of the light-coloured thread-like areas turned out to be softish and has worn more quickly than the rest of the stone.

Stone 6 is quite thin, though it’s face is four by three centimetres in size. I wonder if it might be a hydrogrossular garnet, as it is very smooth, dense and very fine grained. One of the key ways to identify a hydrogrossular garnet is by its waxy feel when it is in the rough. However, tumbling removes that waxy feel so I can’t check it.

Stone 6.

The next stone (Stone 7) is a classic translucent hydrogrossular garnet but there are also a variety of opaque ones, mixed with other minerals, on Gemstone Beach. Unlike the garnets we know as precious gems, hydrogrossular garnets come from dense rock masses, not crystals. Technically, hydrogrossular garnets are a calcium aluminium garnet with hydroxide partially replacing the silica found in other garnets. The first ever identification of hydrogrossular garnet in the world was in 1943 by Colin Hutton, from stones found in Nelson, and it is the most widely spread of the 13 minerals first described from New Zealand. Gemstone Beach is well known for its hydrogrossular garnets, and often they are referred to as the beach’s “gems”. In the TumbleStone Two page on this type of stone, I have described seven types of hydrogrossular garnets that I had found up until that date (June 2022). There are links right at the end of that page to two pages of photos of the types. Stone 6 doesn’t easily fit into any of those types but I wouldn’t rule it out as a hydrogrossular garnet.

Stone 7 is a very good example of a semi-translucent hydrogrossular garnet (what I call Type 2). Holding it up to the sun, some light comes through it.

Stone 7.

Stone 7 held up to the sun.

Stone 8 is an example of my Type 4 hydrogrossular garnet. It is opaque, the sun won’t shine through it.

Stone 8.

Stone 9 is another opaque hydrogrossular garnet, with an interesting spot on one side:

Stone 9.

In the close-up image, the “spot” looks like it’s surrounded by a ring of white crushed quartz that breaks through to a rough surface. However, all of the stone is very smooth, including that area.

Stone 10 is another Type 4 hydrogrossular garnet but with more opaque brown mineral in it than Stones 8 and 9.

Stone 10.

Stone 11 is what I call the “porcelain” type of hydrogrossular garnet. It is an opaque stone that looks and feels like porcelain china, often having fine blue-green veins. There’s a line of broken material down the middle of the stone – it can barely be felt and the stone has polished well.

Stone 11.

I initially did not think this type of stone (Stone 11) was hydrogrossular garnet. I have checked with rockhound groups online, and a number of people have identified it as including hydrogrossular garnet.

Finally, I am unsure whether Stone 12 is another hydrogrossular garnet or a quartz with mineral inclusions. It is not uncommon for me to be doubtful about identification. However, it is the nature of the thin veins within Stone 12 that make it more likely to be quartz in my mind.

Stone 12.

The next Post features another 12 of the Gemstone Beach stones I polished for Michelle.

Gemstone Beach.

Gemstone Beach.

Gemstone Beach, looking northwest.

Stones on Gemstone Beach.

Stones 1 to 10, the larger ones.

Stones 11 to 20.

Stones 21 to 30, the smaller ones.

Relative size of Stones 1 and 30. $2 coin is 2.8cm across.

In this Series of Posts, 30 recently polished stones are examined – they were found on the coastline that runs north from Gemstone Beach near Orepuki in Southland, New Zealand. Many interesting and beautiful stones can be found here, brought down from the mountains of Fiordland by the Waiau River. This Series also illustrates some of the challenges a tumble polisher faces to obtain a completely smooth and well-polished stone. Part 1 in this Series of Posts described Stones 1 to 5, with the following Parts dealing with another five stones each. The five stones featured here are smaller than the first 20 and getting good clear photos of them can sometimes be more difficult as a result.

Stone 21 is a light green argillite with tiny lighter-coloured trace fossils in it. Locals often refer to these as “fossil worm cast” stones.

Stone 21, Side A

Stone 21, Side B

This Post provide some details on argillite, a hardened mudstone. Argillite stones with trace fossils in them are reasonably common on and near Gemstone Beach (and can be found elsewhere in New Zealand as well). Trace fossils are not fossils of an animal itself but of something they have left behind them, like burrows or tracks. Stones Gn40 to Gn62 in this Post are interesting examples of trace fossil argillite stones and their diversity. A small trace fossil stone is in the TumbleStone Hall of Fame. Returning to Stone 21, the bottom half of the stone has markings on it that may not be trace fossils in the usual sense but be ripples in the sediment from sea currents or from a fish swimming by.

The process of tumble-polishing does not always lead to argillite stones with a high polish. However, it removes the dull weathered surface so that things like trace fossils can be clearly seen, even when the stone is dry. I tend to tumble trace fossil stones in 400 grit, followed occasionally with a 600 grit tumble, then the polish stage. Skipping the use of the coarser grits helps to preserve the trace fossils as they appear on the surface, though some small holes and scratches may remain.

Stone 22 is a small jasper (I think) of lively brown colour, with an interesting milky quartz vein and a few very thin transparent veins.

Stone 22, Side A

Stone 22, Side B

There appear to be inclusions of quartz and maybe mica which interrupt a smooth surface. The largest vein also has some holes in it, as can be seen especially on Side A. To remove these using tumbling would have made the stone very small – it is currently just under 2 cms at its widest – with no guarantee that all the “imperfections” would be absent.

A remarkable little pebble, Stone 23 contains a small vein with tiny brecciations filling it. It’s like a glimpse into a hidden shrunken world.

Stone 23, Side A

Stone 23, Side B

As noted in relation to Stone 1, breccia are angular fragments of stone that have been compressed together in a fine-grained matrix. There are a number of different causes for brecciation, such as the accumulation of rock debris from weathering or erosion and the fragmentation of rock in a contact area between two faults (see GeologyScience.com). The brecciation in Stone 23 could have been caused by pressure stresses in the rock, pushing and pulling resulting in fragmentation then the creation of a vein into which maybe quartz has filtered, cementing the fragments. Again, as is illustrated clearly on Side B, the amount of tumbling necessary to produce a smooth surface would have resulted in a very small stone. Limiting the use of coarse grit means that a small scratch remains, marring the end product, but we have a fascinating little stone to admire.

Stone 24 is a small milky quartz.

Stone 24, Side A

Stone 24, Side B

The B side shows the result of an impact on the stone. This type of line often goes deep into a stone and so cannot be removed by tumbling without destroying the stone itself. Wikipedia notes that milky quartz is a very common variety of crystalline quartz. “The white color is caused by minute fluid inclusions of gas, liquid, or both, trapped during crystal formation.” Stones W1 to W3 in this Post are other specimens of milky quartz from Gemstone Beach, in the rough unpolished state (but still very smooth). This type of quartz stone tumble polishes very well.

Stone 25 has distinct ribbons of green that caught my eye on the beach (apologies that the photos are not sharper).

Stone 25, Side A

Stone 25, Side B

The banding in this stone is a mix of mudstone (argillite) and sandstone (including some tiny quartz grains), very similar to Stone Gn14 in this Post. In such cases, I usually make sure that I do a 600 grit tumble before putting the stone to polish, to help the coarser material to polish better.

The final Post in this Series (not yet published) deals with Stones 26 to 30.

Fossickers on Gemstone Beach.

Looking west from Gemstone Beach towards the mountains of southern Fiordland.

Te Waewae Bay waves.

Te Waewae Bay stones, just northwest of Gemstone Beach.

Stones 1 to 10, the larger ones.

Stones 11 to 20.

Stones 21 to 30, the smaller ones.

Relative size of Stones 1 and 30. $2 coin is 2.8cm across.

A great diversity of interesting and beautiful stones can be found on the coastline that runs north from Gemstone Beach near Orepuki in Southland, New Zealand. In this Series, 30 recently polished stones from that beach are described. They also illustrate some of the challenges a tumble polisher faces to obtain a completely smooth and well-polished stone. These 30 stones were selected from the smaller stones in batches tumbled in two 3lb barrels. As a result of looking closely at these stones, I realise the need to pay more attention to my inspection of stones before they pass onto the next stage of tumbling. And I need to re-examine my use of cushioning filler in the latter stages of the tumbling process. Part 1 in this Series of Posts described Stones 1 to 5, Part 2 dealt with Stones 6 to 10, and Part 3 examined Stones 11 to 15. The five stones featured here are slightly smaller than the first 15.

Stone 16 is perhaps one of the most beautiful four stones of the 30, and in addition it is among the best polished. It is a hematite jasper with some white quartz in it.

Stone 16, Side A

Stone 16, Side B

I have noticed that the brightest of the red jaspers on Gemstone Beach tend to have hematite in them. The following is taken from a November 2023 TumbleStone Blog Post on a Gemstone Beach hematite jasper: As Britannica notes, hematite is a heavy and relatively hard oxide mineral, ferric oxide (Fe₂O₃). It makes up the most important iron ore because of its high iron content (70%) and its abundance. Its name is derived from the Greek word for “blood,” alluding to its red colour. I recently read the following comment made by Tim Weglarz on the “Great Lakes Rocks & Minerals” Facebook Group: “The grey metallic bands and red coloration… of jasper is from hematite. When hematite occurs as megascopic flakes, it is opaque and metallic. When it occurs as microscopic flakes dispersed in silica, it is translucent and blood red… The red jasper… has much smaller amounts of much finer grained hematite than the opaque metallic bands.” See “H is for Hematite Jasper” in this Post for a brief description of hematite jasper generally.

Stone 17 has some fascinating veins, white and green, which caught my eye on the beach. It is tempting to think it is jasper but not all dark red rock is. The dark red is due to the presence of iron oxide, and this can occur in a number of rock types. Stone 17 has lots of tiny quartz crystals in it, so it may be a form of quartzite.

Stone 17, Side A

Stone 17, Side B

Much of Stone 17 has not taken a good polish and it lacks shine but the veins are clear and detailed.

Stones 18 and 19 also did not tumble polish well. Stone 18 is very likely to be a jasper, and sometimes jaspers like this, with lighter coloured material, do not polish well.

Stone 18, Side A

Stone 18, Side B

An idea of varieties of jasper and difficulties in tumble polishing them can be found in “Diane’s Stone, and an Introduction to Jasper”.

Stone 19 has a variety of material in it, some of which appears crumbly and did not not take a shine.

Stone 19, Side A

Stone 19, Side B

It was the pink in the stone that caught my eye on the beach, but I have mixed success in polishing such stones. Usually I am able to cull crumbly stones at an early stage in the tumbling process through the inspection I undertake between stages. However, sometimes my optimism that a stone will turn out to be ok overrides my critical judgement.

Stone 20 is a gorgeous little jasper that I struggled to get good images of. Perhaps the sunlight was not bright enough, or maybe the slight roundness of the surfaces introduced subtle reflections. Unlike most of the other stones, which had two main faces, Stone 20 has three main faces.

Stone 20, Side A

Stone 20, Side B

Stone 20, Side C

Hematite is again present in the stone, and I suspect it contributes to the bright yellows, oranges and reds.

Part 5 in this Series examines Stones 21 to 25.

Stone fossickers on Gemstone Beach.

Gemstone Beach, looking northwest.

Te Waewae Bay beach, near Waimeamea River mouth.

Waves sweeping up Gemstone Beach, tumbling stones.

Stones 1 to 10, the larger ones.

Stones 11 to 20.

Stones 21 to 30, the smaller ones.

Relative size of Stones 1 and 30. $2 coin is 2.8cm across.

In this Series, 30 recently polished stones from Gemstone Beach/Te Waewae Bay are described. They illustrate the great diversity and beauty of stones that can be found on this beach, as well as some of the challenges a tumble polisher faces to obtain a completely smooth and well-polished stone (if that’s their aim). These 30 stones were selected from the smaller stones from batches tumbled in two 3lb barrels. Initially I thought all the stones in these two batches ended up nice and smooth. However, looking at their photos, I noticed tiny holes, bruises, scratches and rough patches on many of them. I need to pay more attention to my use of cushioning filler in the latter stages of the tumbling process. Part 1 in this Series of Posts described Stones 1 to 5 and Part 2 dealt with Stones 6 to 10. The five stones featured here are slightly smaller than the first ten.

Stone 11 is a small grey stone with a faint hint of blue.

Stone 11, Side A

Stone 11, Side B

When I saw it on the beach, the thin dark veins stood out. Later, while turning the stone for photographs, sunlight glinted off a couple of small areas, probably mica crystals. Some can be seen at the bottom right in the close-up of Side A above.

Stone 12 is a variation of spotted argillite, as is Stone 3 (see Part 1) and Stone 14 (below).

Stone 12, Side A

Stone 12, Side B

Stone 12 is darker in colour than Stone 3, and its “spots” are slightly more clearly defined. There is quite a range of spotted argillites on Gemstone Beach.

Stone 13 is an astonishing cluster of small white spots. They are packed tightly together.

Stone 13, Side A

Stone 13, Side B

This is likely to be a volcanic stone, originally full of tiny gas bubbles. Those bubble holes (“vesicles”) were infilled slowly by a white mineral as hot water flowed into them. These white “spots” are called “amygdales” (or “amygdules”), from the Latin and Greek words for almond, reflecting the almond-shape of many such spots. Stones W30 to W33 in this Post are other examples of amygdaloidal stones from Gemstone Beach, and a more detailed explanation of their formation follows them.

Stone 14 has some similarities to Stone 3 – a dark green fine-grained sedimentary stone with seemingly out-of-focus light-coloured spot-like patches.

Stone 14, Side A

Stone 14, Side B

They are both most likely to be types of spotted argillite (along with Stone 12). Stone 14 also has some very fine veins in it, some dark and some light. At first sight, it is tempting to think Stone 14 could be a “variolite”, because of its appearance. Variolites contain small spherical or globular structures, called varioles, in a fine-grained matrix. Varioles are lighter coloured than the host rock and the photo of a specimen on Wikipedia looks very similar to Stone 14. However, variolites are volcanic in origin, usually basaltic. Mindat notes that varioles have quite a different origin than spherulites, which are also small rounded bodies that commonly occur in igneous rocks (such as spherulitic rhyolite, as can be found at Slope Point – see, for example, the second stone in this Post).

Stone 15, like Stone 4 and Stone 9, is volcanic in origin with light-coloured crystals in it. Unlike Stone 4, the crystals are densely packed and in contrast to Stone 9, the surrounding rock material is not as dark.

Stone 15, Side A

Stone 15, Side B

The tiny often oblong crystals in the stone are fascinating, and scattered amongst them are some black and some silver (mica?) crystals:

Greater close-up of Side A

Greater close-up of Side B

The next Post in this Series examines Stones 16 to 20.

Part of Te Waewae Bay coast, from Gemstone Beach in south to Waimeamea River mouth and lagoon, my fossicking area. Source: Google Maps.

Mouth of Taunoa Stream, not far from carpark.

Hidden house, Gemstone Beach.

Gemstone Beach stones.

Stones 1 to 10, the larger ones.

Stones 11 to 20.

Stones 21 to 30, the smaller ones.

Relative size of Stones 1 and 30. $2 coin is 2.8cm across.

In this Series, I present 30 recently polished stones from Gemstone Beach/Te Waewae Bay. They illustrate the great diversity and beauty of the pretty stones of this beach, as well as some of the challenges a tumble polisher faces to obtain a completely smooth and well-polished stone (if that’s their aim). These 30 stones were selected from the smaller stones from batches tumbled in two 3lb barrels. Part 1 described Stones 1 to 5. The next five stones, featured here, are slightly smaller than the first five.

Stone 6 is a mix of colours and shapes. On the beach, the bright sweep of opaque white on Side A caught my eye, then the green (most likely epidote), then, upon closer inspection, the intriguing veins.

Stone 6, Side A

Stone 6, Side B

This is a good example of a small stone that reveals more and more as you look closer at it. Though tiny holes are also among the things revealed.

Stone 7 is an example of a stone that from a distance appears to have a simple makeup – some light-coloured patches and some slightly darker patches.

Stone 7, Side A

Stone 7, Side B

But closer inspection reveals an intricate mosaic of what could be tiny crystals in an irregular latticework pattern. It’s an amazing and beautiful stone, but I don’t know what kind it is. A few tiny scratches can also be seen.

Stone 8 has contrasting sides. It’s a type of quartz, I call it a sugary quartz because of the small granular-like crystals that make it up. Side A has a brown hue, Side B has a whiter hue.

Stone 8, Side A

Stone 8, Side B

The difference in colour will be due to variation in the presence of a brown mineral, most likely iron oxide. Stones of this “sugary” composition can be hard to get completely smooth through the tumbling process, with tiny grains coming loose from the surface. However, I like how they look and have had success with a number of them.

A small black and white volcanic stone, Stone 9 is full of amazing tiny white crystals.

Stone 9, Side A

Stone 9, Side B

The crystals are elongated and appear to float throughout the black material. Generally speaking, the longer it takes for volcanic rock to cool, the larger the crystals in it will grow, having longer time to form. In this Post on igneous stones from Gemstone Beach, Stones W43 to W56 illustrate the diversity of white crystal shapes and sizes that can be found.

Stone 10 looks like a pale-coloured mudstone, but it has some interesting dark veins or lines in it. These are likely to be dendrites, thin branching lines of crystals, often of some variety of manganese oxide (or iron), that grow over the surface of a stone. They are found in cracks or along bedding planes. The word “dendrite” is from the Greek word for “tree”, referring to its branching appearance.

Stone 10, Side A

Stone 10, Side B

Mindat has some good photos of dendrites and Sandatlas has a technical explanation of their growth. Thornton provides some NZ examples of dendrites in agates in her book “Gemstones” (page 15 here). Dendrites are often given as examples of “pseudofossils”, natural objects that may be mistaken for fossils of, for example, a plant leaf.

Part 3 in this Series examines Stones 11 to 15.

Orepuki, Southland.

Gemstone Beach, in front of the carpark.

Looking northwest from in front of the carpark.

Gemstone Beach stones.

Stones 1 to 10, the larger ones.

Stones 11 to 20.

Stones 21 to 30, the smaller ones.

Relative size of Stones 1 and 30. $2 coin is 2.8cm across.

Just before Christmas, I finished polishing some of the stones I had collected from Gemstone Beach and nearby in early 2023. They were tumbled in two 3lb barrels, the final stage for each batch being a tumble in tin oxide polish for just over two weeks, followed by burnishing in borax (for three days for one barrel, for five days for the other). Most of the stones would have been tumbled prior to this in 600 grade silicon carbide grit; all of them were tumbled in 400 grit before that; and some of them, those needing the most smoothing, would have been first tumbled in 220 grit.

In this Series of Posts, I present 30 of the smaller stones, to show their character as well as the difficulty of tumble-polishing. Throughout the stages of tumbling, I carefully sort through stones to try to make sure that they are as smooth as possible before they go on to the polish tumble. At first glance, I thought all the stones in these two batches were nice and smooth, and that they ended up well polished. However, looking at these photos, I can see the need for me to be even stricter before the final stage, as tiny holes, bruises, scratches and rough patches are apparent on many of the stones. I need to pay more attention to cushioning filler – I am currently reducing my use of plastic beads and using very small stones instead. I didn’t seem to get the balance of filler to stones quite right with these batches. Nevertheless, what is also apparent is the often complex and beautiful character of these stones, truly natural wonders from a Southland beach.

The first five stones are the larger of the 30, though the largest, Stone 1, is only about 5 cms wide. It is an example of a stone made up of lots of different little bits. In terms of appearance, it has many shades of grey. In constitution, it is a breccia, meaning that it consists of angular fragments of stone that have been compressed together in a matrix – see University of Auckland Geology. [If the fragments, known as clasts, were rounded, it would be a conglomerate, the fragments having been eroded by travel from their source before being compressed.]

Stone 1, Side A.

Stone 1, Side B.

Some of the fragments are likely to be argillite, a mudstone, but there are a lot of other little things in there too, various grains and crystals. Some of the crystals reflect the light when held at an angle. This diversity of material in the stone also explains why it did not take a uniform polish – for example, some of the fragments, grains or crystals will be softer.

Stone 1 is a dark stone, but Stone 2 is much lighter in appearance (though with a few dark patches).

Stone 2, Side A.

Stone 2, Side B.

One of the black patches on Side B is particularly striking. Again, this stone is a breccia, with the dark patches being angular clasts. Much of the light-coloured material could be quartz of some form. Quartz is a form of silica and is among the most common of all rock forming minerals. It is found in a wide variety of types in different kinds of rocks. It tends to tumble polish well.

Stone 3 is spotted argillite, a fine-grained mudstone. The “spots” are not perfect, many are not well-formed, but the colour variation they introduce leads to an interesting visual pattern. On Gemstone Beach, argillite is often a solid green colour, but this is an example of one of the variations that occurs. The green of Stone 3 is highly likely to be caused by the mineral epidote which in New Zealand is widespread in veins in greywacke, schist and granite. Epidote is in fact the main mineral in the iron-rich mudstones of Otago and Southland, including argillite.

Stone 3, Side A.

Stone 3, Side B.

Stone 3 has come through the tumbling process reasonably well, though there is a slight scratch on Side B. In this Post on green stones on Gemstone Beach, 12 other specimens of spotted argillite are presented (Stones Gn20 to Gn31). I suggest there that “spots” occur when argillite comes under increased pressure and heat, more than is usual for a sedimentary rock. During this process, certain minerals become concentrated in specific areas.

Stone 4 is probably of igneous origin, most likely volcanic. It is quite different from the previous three.

Stone 4, Side A.

Stone 4, Side B.

It is mainly dark, yes, and has a mixture of material in it, including white crystals (or are they clasts?), but it also has some intriguing subtle linear shapes. It was those shapes that caught my eye on the beach, and it is their existence that defines the individuality of the stone.

I found Stone 5 on 12 April 2023 (see this Post). It appears to be made up primarily of black and white crystals, with minerals providing pastel colour patches of orange/pink and light green.

Stone 5, Side A.

Stone 5, Side B.

The black crystals help create contrasting halves in the stone, with the pastel colours providing a subtle delicacy. The orange/pink is likely to be due to the presence of orthoclase feldspar, a potassium-bearing member of the alkali feldspar family – it is orthoclase feldspar that gives granite its pink component. The green patches are likely to be caused by the mineral epidote (mentioned in relation to Stone 3 above). Stone 5 has tumbled well, though Side A has some tiny rough areas.

The next Post in this Series examines Stones 6 to 10.

The final in this Series, this stone contains the same green-hued mineral as Stone #11. It’s most likely epidote, in quartz. In Stone #11, the green is in patches; in Stone #30, there are some striking thin veins circling it, which caught my eye when I spotted the stone on Gemstone Beach.

Stone #30, Side A.

Stone #30, Side B.

The stone is more spherical, less flat, than most of the others in this Series. There is a tiny hole on Side A and a thin scratch on Side B – maybe incurred during the tumbling process. Generally, a quartz stone like this one will tumble-polish very well.

Go to Stone #1 in the Stone of the Day Series for November. Go to the Series Index.

Many beach stones in New Zealand are dark in colour, with the main exception of white quartz. Lighter coloured stones stand out and draw the fossicker’s eye on the beach. This stone is an example of a lighter coloured one, with a white quartz vein in it. The close-ups reveal a range of light coloured minerals in it, along with some darker red patches of iron oxide.

Stone #29, Side A.

Stone #29, Side B.

Tumble polishing can be an inexact art. You cannot always obtain a perfect smooth polish. Close-ups often reveal tiny blemishes on a stone that are not picked up by the unaided eye. Stone #29 has a couple of tiny scratches in it, and some small bits have not taken a good polish. A return to a 400 grit tumble followed by a 600 grit stage then polish again might improve it.

Go to Stone of the Day #30. Go to the Series Index.

Another tumble-polished black and white stone from Gemstone Beach – the other black and white ones in this Series are #2, #12 and #13. Most similar to #12, it contains some dark gray pieces not in that stone.

Stone #28, Side A.

Stone #28, Side B.

Despite being tumbled in a fine 600 silicon carbide grit for at least a week before going into the polish tumble stage, the stone has a number of small rough areas. At least some of these are likely to be due to some softer minerals being present. I am often surprised to see such rough areas when looking at the close-up photos – they are not easy to pick up by eye when inspecting the stones between stages.

Go to Stone of the Day #29. Go to the Series Index.