Tag: Riverton

Twelve Stones, Part Four

Part One of this Series, about 12 stones, can be found here. The four Posts in the Series each describe the characteristics and origins of three different stones. This Post describes Stones #10 (from Riverton), #11 (from Birdlings Flat) and #12 (from Hokitika).

1-6 stones 2227-12 stones 222

10) Stone #10 Whitish Quartzite stone with Clear Silica Inclusions, found at Riverton.

I have explained the origins and characteristics of Quartzite in relation to Stone #7 and have provided photos of Quartzites from Birdlings Flat in relation to Stone #8, both in Post Three. Quartzite stones can be found in a number of locations in the South Island. They can have a wide range of colours. One of their frequent characteristics is the clear inclusions of silica running through the stone. Quartzites polish outstandingly, due to their hardness and colours.

For the location of Riverton, see the end of the section on Stone #2 in Part One.

11) Stone #11 Banded Agate, found at Birdlings Flat.

Malcolm Luxton is a collector of Agates. He lives in Ashburton, close to New Zealand’s greatest agate-bearing locality of mid-Canterbury. In his excellent book, “Agates of New Zealand” (2015), he provides hundreds of photos of cross-sections of Agate rocks and stones he has collected from throughout New Zealand.

Cover of Malcolm Luxton (2015) “Agates of New Zealand”, Agate Orphanage Press, Ashburton.
Moss agate, Woolshed Creek, Canterbury – Page 33 of Luxton’s (2015) “Agates of New Zealand”
Banded agate, Stew Point Station, Canterbury – Page 91 of Luxton’s (2015) “Agates of New Zealand”
Banded agate, Rakaia Gorge, Canterbury – Page 230 of Luxton’s (2015) “Agates of New Zealand”
Agate in dark rhyolite, Woolshed Creek, Canterbury – Page 192 of Luxton’s (2015) “Agates of New Zealand”
Coloured Canterbury beach agate – Page 254 of Luxton’s (2015) “Agates of New Zealand”

Luxton offers this explanation for the origin of Agate:

An agate…is a stone that formed as a secondary filling in the various shaped cavities generated or forged within…lava flows. Initially these cavities were created by trapped gases or liquids or by geological processes that produced cracks or ruptures. The secondary filling permeated the lava as a silica-rich solution, and…solidified inside these cavities, thus replicating the shape of its magmatic womb. If additional materials were present, either in the silica-rich solution or growing in the cavity prior to its introduction or introduced as by-products from the surrounding lava, those minerals may have been responsible for structures, assemblages and colours (page 16).

Luxton notes that much Agate material is discharged by Canterbury rivers into the sea and some of it is cast back onto more than 100 kms of Canterbury beaches. The movement of Agates by northerly coastal currents “accounts for the notoriety of Birdlings Flat as an agate-collecting destination” (Luxton, 2015, page 250). He then refers to Vince Burke’s collection in the Birdlings Flat Gemstone and Fossil Museum.

Wall display of rocks and their origins, including Agates,Birdlings Flat Gemstone and Fossil Museum
Agate shelf display, Birdlings Flat Gemstone and Fossil Museum
Coloured Agate cross-sections, Birdlings Flat Gemstone and Fossil Museum
Large Agate rock, Birdlings Flat Gemstone and Fossil Museum
Birdlings Flat Gemstone and Fossil Museum
Birdlings Flat Gemstone and Fossil Museum
Birdlings Flat Gemstone and Fossil Museum

Upon my visits to Birdlings Flat, I have collected a few Agates, mainly quite small ones, though my wife Petra is much better at spotting them than I am! Some of the Agates I have found are just plain cloudy silica, some are banded to some extent, some have a little colouring.

Some of the Agates I have collected at Birdlings Flat
Most of the Agates collected are small, with only the occasional larger one
A “blue” Agate stone
A nice moss Agate stone from Birdlings Flat
The only Agate with bright colour that I have found
Some Agates have a whitish tinge on the outside
Banded Agate
Nice little banded Agate from Birdlings Flat

For the location of Birdlings Flat, see the end of the section on Stone #8 in Part Three.

12) Stone #12 White Quartz, found at Hokitika.

Quartz is originally a clear crystal. When subject to heat and pressure, and when water is introduced into it, it becomes white in colour, the colour of the common white “Quartz” stone found plentifully on beaches in New Zealand. However, strictly speaking, this is “Quartzite” rather than “Quartz”, though the latter term is the most common for this white stone. For that reason, and in order to distinguish it from Stones #8 and #10, I will call it “Quartz”.

Southland Museum display on Quartz. Top centre is a clear piece of Quartz
The clear Quartz in the Museum display

When walking beaches, it is the bright white Quartz stones that seem to claim the first attention of the collector’s eye. I have collected and polished many white Quartz stones from the beaches of Southland, Canterbury and the West Coast. And it is the West Coast where perhaps the best examples can be found, perhaps due to the closeness to the Quartz source, in the Southern Alps. 

Dinner plate full of polished white Quartz stones
Part of a batch of Hokitika stones in the process of being polished
Held up to the light, some white Quartz stones are semi-translucent

Stone #12 was found on the beach just on the south side of the Hokitika River, less than five kms from Hokitika town. I visited there on a dull, cold, rainy day in June 2016. The beach was quite sandy but receding waves revealed drifts of stones. There were signs of coastal erosion, with flax plants being undermined and uprooted, and the end of the gravel road had been washed away.  

Hokitika on the West Coast of the South Island
Signs of coastal erosion near Hokitika. June 2016.
Driftwood on the beach.
Stones being revealed by the receding waves.
Drifts of stones on the beach near Hokitika.
Mouth of the Hokitika River, looking north at Hokitika on the far shore.
A large white Quartz stone found at Rapahoe Beach, just north of Greymouth, on the same trip. I had to leave this there as I was travelling home by plane and taking other stones with me.
What Hokitika is most famous for – its greenstone carvers.

Location of Hokitika (click on image below, left), and location of beach near Hokitika where Stone #12 was collected (below, right) (source: Google Maps):

This brings us to the end of this series of Posts.

Twelve Stones, Part Three

This Post describes Stones #7 to #9 of the 12 (Part One dealt with Stones #1 to #3 and Part Two with Stones #4 to #6):

7-12 stones 222

7) Stone #7 Red-Stained Quartzite, found near Budleigh Salterton, England.

On two recent visits to England, in 2017 and 2018, I went to a coastal village of about 5,000 inhabitants called Budleigh Salterton in Devon, not far from Exeter. The Doomsday Book records that salt panning was of great importance here, and it may have been as far back as Roman or even Iron Age times, hence the origin of the name “Salterton”. The beach, three miles (nearly five kilometres) in length, has a distinctive mix of stones, many deriving from the Budleigh Salterton Pebble Bed which outcrops in the cliffs there. 

Looking south-west towards the village of Budleigh Salterton
Looking north-east along the beach at Budleigh Salterton
Budleigh Salterton beach huts
Beach huts and red cliffs at Budleigh Salterton

The layers of pebbles found in the cliffs at Budleigh Salterton originated over 400 million years ago when sandstones formed under desert conditions in the place in France we now call Brittany. During the Triassic period, these rocks were eroded and transported by vast rivers  across what later became the English Channel to form the Budleigh Salterton Pebble Beds. The pebbles then fell onto the beach and have been transported eastwards by the sea, well beyond Budleigh Salterton. 

The  East Devon and Dorset Coast, known as the Jurassic Coast, has become a World Heritage Site due to the geology of the area. In 95 miles (150 kms), 185 million years of earth history are on display in the coastal cliffs. Older Triassic rocks (between 251 million and 200 million years old) give way to Jurassic rocks (200 million to 145 million years old) and younger Cretaceous rocks (145 million to 66 million years old). 

Part of an Information Panel in Budleigh Salterton
Information Panel section on the pebble beds
Red pebble cliffs
Dry stones on Budleigh Salterton beach
When the stones are wet, their colours become apparent. In the middle is a stone with dark red speckles, just like Stone #7
Stone #7 is at bottom centre, just off the beach

The British geologist Ian West has a very interesting web page on Budleigh Salterton and the surrounding area (even though it can be difficult to read in places). There he states that the dominant pebbles in the Budleigh Salterton Pebble Bed are quartzite (if you go to this link, click again on it to enlarge the writing at the bottom of the photo). Quartzite is  a very hard durable metamorphic rock composed almost entirely of quartz. It forms when a quartz-rich sandstone is altered by the heat, pressure, and chemical activity of metamorphism. These conditions recrystallize the sand grains and the silica cement that binds them together. The result is a network of interlocking quartz grains of incredible strength. Impurities in Quartzite can cause it to be yellow, orange, brown, green, or blue. The presence of iron results in pink, purple or (as with Stone #7) red. 

Location of Budleigh Salterton in south-west England (source: Google Maps):

Budleigh Salterton location

8) Stone #8 White-Grey Quartzite.

I collected this stone at Birdlings Flat, Canterbury, a beach that I try to visit at least a couple of times each year because of the Quartzites, Jaspers and Agates (see Stone #11) to be found there. Birdlings Flat is the beach immediately south of Banks Peninsula, part of Kaitorete Spit, an enormous barrier gravel bank  which lies between Lake Ellesmere and the sea. Stones washed down from the Alps by Canterbury rivers are swept northwards along the coast and deposited here.

Where Birdlings Flat beach meets with Banks Peninsula
Looking southwest along Birdlings Flat beach
The waves are powerful and unpredictable, especially at the Banks Peninsula end
The Birdlings Flat beach is part of the 25 km long Kaitorete Spit which consists entirely of stones
Looking for stones about eight kilometres along Kaitorete Spit

As mentioned in relation to Stone #7, Quartzite is a very hard durable  metamorphic rock composed almost entirely of quartz. Many different coloured Quartzite stones can be found at Birdlings Flat, as attested by the collection to be found at the Birdlings Flat Gemstone and Fossil Museum, which I have visited a number of times.

Part of the Quartzite Collection at the Birdlings Flat Gemstone and Fossil Museum. At top right is a large white-grey stone, with a fault through it. Photos with permission
Some white-grey Quartzite stones similar to Stone #8 can be seen on the lower row
Another part of the Quartzite Collection at the Birdlings Flat Gemstone and Fossil Museum
More Quartzite stones, Birdlings Flat Gemstone and Fossil Museum
Stones in Birdlings Flat Gemstone and Fossil Museum, including Quartzites

Stone #8 is one of a number of white-grey Quartzites I have found at Birdlings Flat. The large bands of white and grey provide a striking contrast, making this stone particularly attractive.

Stones collected at Birdlings Flat, including some white-grey Quartzites
Two Quartzites from Birdlings Flat
Two good-sized tumble-polished Quartzites from Birdlings Flat
A darker white-grey Quartzite
Quartzite with more white than grey
A white-grey Quartzite found and polished by Petra

There are a number of previous TumbleStone Posts about Birdlings Flat. These include: Birdlings Flat Gemstone and Fossil Museum;  Seven Types of Stones Collected at Birdlings Flat; Selection of Online Sources about Birdlings Flat; and Information on Birdlings Flat from Books.

Location of Birdlings Flat (source: Google Maps):

Birdlings Flat location

9) Stone #9 Unknown stone, found at Riverton.

I picked up this interesting little stone at Henderson Bay, Riverton Rocks. I initially wondered if it might be a piece of petrified wood, given its pattern and texture. Some agatised wood (see photos below) that I have seen has some similar patterns. Petrified wood forms when wood is buried by sediment and protected from decay by oxygen and organisms. Groundwater rich in dissolved solids flows through the sediment, replacing the original wood material with, for example, silica, calcite, or pyrite. Agatised wood has been petrified by agate, a form of chalcedony or microcrystalline quartz. However, the agatised wood I have seen tends to be quite glassy when polished, something absent from this stone. 

Agatised wood specimens at the Birdlings Flat Gemstone and Fossil Museum
Agatised wood, from a YouTube clip https://www.youtube.com/watch?v=Rxc1j6QNPvI

In March 2017 I bought a piece of petrified wood from Hettie’s Rock and Crystal Shop in Akaroa on Banks Peninsula.

Petrified wood bought at Hettie’s, Akaroa, March 2017
Hettie’s Rock and Crystal Shop, Akaroa
Another side of the same piece of petrified wood

I have also seen petrified wood at Curio Bay, about 130 kms east of Riverton. 

Curio Bay, Catlins Coast, Southland
Information Plaque about Curio Bay
The steps down to Curio Bay
Looking down on Curio Bay from the top of the steps
Trunk of a petrified tree at Curio bay
Petrified wood in the rocks at Curio Bay
Petrified wood in the rocks at Curio Bay. My foot for scale
Petrified wood in the rocks at Curio Bay

On the basis of what I have seen, I am unsure whether Stone #9 is agatised wood or some other form of petrified wood, or something entirely different. I have more unidentified stones than identified ones in my collection. [Later I came to the view that this stone is much more likely to be a mix of quartz and a black mineral, not any type of petrified wood.]

I found Stone #9 at Henderson Bay, the last of the Bays that make up Riverton Rocks, the part of Riverton that is made up of holiday homes. My grandparents owned a “crib” (“bach” to North Islanders of New Zealand) at Henderson Bay, up on the hill overlooking the sea, and when I was a boy my family spent two weeks every summer on holiday there. 

Henderson Bay, Riverton Rocks, September 2018 – the road continues on to the Back Beach
Henderson Bay, February 2016
Henderson Bay, looking back at the steps
Argillite rocks at Henderson Bay, stones above the high tide mark on the beach
Drift of stones, Henderson Bay
Henderson Bay stones
Henderson Bay stones

Location of Henderson Bay and Back Beach, Riverton (source: Google Maps):

location Riverton bays333

Part Four is the final Post in this series, dealing with Stones #10, #11 and #12.

Twelve Stones, Part Two

I recently presented 12 tumble-polished stones to Tony in appreciation for his support when I undertook work with him in the dairy industry. Part One of this series of Posts described Stones #1 to #3. This Post deals with the characteristics and origins of Stones #4, #5 and #6, and later Posts will examine Stones #7 to #12. 

These are the 12 stones:

1-6 stones 2227-12 stones 222

4) Stone #4 Pink Granite

This stone was found at Riverton in February 2018. Granite is a coarse-grained igneous rock, made up of quartz, feldspar and mica. Its grains are large enough to be seen by the unaided eye. Pink Granite is given its colour by a larger proportion of potassium feldspar. Granite is found exposed at various places on Stewart Island and the western part of the South Island. It can be seen along the coast between Colac Bay and Orepuki in Southland, and stones of Pink Granite can often be found on southern beaches. Click on the photos below to see their captions.

Display of Granite stones, Riverton Museum. Photo with permission of Museum staff..
Page 92 of “The Illustrated Encyclopedia of Minerals, Rocks & Fossils of the World” by John Farndon and Steve Parker (2015).
Page 34 of “Rock and Gem: The Definitive Guide to Rocks, Minerals, Gems and Fossils” by R.L. Bonewitz (2008).

5) Stone #5 Finely Banded Rhyolite(?)

This stone was found at Orepuki, Southland, on Gemstone Beach in April 2016. I have collected a number of such stones before on southern beaches and find them fascinating as they conjure up the image of cosmic gas trails in faraway starfields. A fellow stone collector once told me they were Rhyolite but it is difficult to confirm this from the various online and published sources on Rhyolite, maybe due to the distinctive pattern on these particular stones.

Rhyolite is very similar in chemical composition to Granite. But while Granite has crystals that are generally easy to see, in Rhyolite the crystals are often too small to see. This is due to the more rapid cooling of the Rhyolite lava at the earth’s surface compared to granite’s slower cooling magma within the earth.

Examples of other Rhyolite stones found at Orepuki or Riverton:

Rhyolite stone just picked up from the beach
Rhyolite stone after one stage of tumbling
Three polished Rhyolite stones from southern beaches
Top centre is the Rhyolite Stone #5, washed after being found on Gemstone Beach at Orepuki

Orepuki is a small village on a sparsely settled part of the southern coast. Gold was mined in the district during the last two decades of the nineteenth century, and in the 1880s the southernmost Chinese settlement in the world was to be found there. The beach just to the north of Orepuki is called Gemstone Beach – it is said that semi-precious gems such as garnet, sapphire, jasper, quartz and nephrite can be found on the beach, along with hydrogrossular stones and argillite stones containing fossil worm casts. (The garnets, sapphires and nephrite are extremely rare.) Gold can also be found in patches of black sand at low tide.

Gemstone Beach, Orepuki, Information Panel – some of the stones mentioned are very rare and are not usually found
Gemstone Beach, Orepuki, September 2018, looking south
Gemstone Beach, Orepuki, September 2018, looking north
Stone collectors, Gemstone Beach, Orepuki
A wide bank of stones at Gemstone Beach – sometimes there are not many stones on the beach
Stones at Gemstone Beach
Washed stones collected from Gemstone Beach – three Rhyolite ones at left and centre bottom. In the middle is a green argillite stone with a lighter coloured fossil wormcast
Information Panel, Round Hilly Track, main area of gold mining near Orepuki
Information Panel detail on Chinese gold mining town

Location of Orepuki (source: Google Maps):

Orepuki location

6) Stone #6 Marble(?)

I found this stone also on a Riverton beach. I don’t know what type of stone this is, but it reminds me of Marble. Marble is formed out of limestone which is subjected to the heat and pressure of metamorphism. It is composed primarily of the mineral calcite and in its pure form is white. However, it can also contain other minerals, such as clay minerals, micas, quartz, pyrite, iron oxides, and graphite, which provide colouring. Veined and patterned Marble, as this stone could be, is often created when a pure white original Marble is cracked or shattered and the spaces between the fragments are filled with other materials.

Page 199 of “Collecting Rocks, Gems and Minerals” by Patti Polk (2016)
From Southland Museum, Invercargill
Maybe another Marble stone collected from Riverton – part of the first batch of stones I polished in March 2016

Stones #7 to #9 are described in Part Three.

Twelve Stones, Part One

I recently presented 12 of my polished stones to a work colleague in appreciation. 

zDSC01427

I took on the job of Assistant to an AB Technician in the dairy industry for three weeks, at the height of the insemination season. This was a completely new experience for me and I enjoyed it a lot, largely due to the support and patience of Tony, the Technician I was assisting. I chose to give him 12 stones because I spent a lot of time preparing the 12 inseminator implements that he regularly used. Below is a photo of inseminators being loaded (a straw of bull semen is loaded into the end of each inseminator, its plug snipped off with scissors, then a plastic sheath is threaded over it to hold in place).

aaa

These are the twelve stones:

1-6 stones 2227-12 stones 222

I am taking the opportunity in this Series of Posts to dig into aspects of different types of stones and the places from which they were collected. This first Post will describe Stones #1 to #3, with the rest dealt with in Parts Two, Three and Four.

1) Stone #1 Dark Red Jasper

I found a rock in April 2016 near Waikaka in Eastern Southland. It was embedded in a farm track on “The Mains”, the farm on which I grew up. Red Jasper is a rock to be found as part of the Waikaka quartz gravels which contain the gold mined in the area between the 1880s and 1920s. There is an old gold dredging pond about 100 metres north of the track. I extracted this large Jasper rock and took it home with me to Karapiro on the plane. Later I broke off a few pieces to tumble-polish. Due to the brittle nature of the rock, I did not completely smooth the stones out before their final polish. (Click on the photos below to view them and see their accompanying captions.)

The farm track on “The Mains” – when it reaches the trees, it crosses the Waikaka River on a bridge. I found the Jasper rock about 30 metres from this point.
I broke a number of pieces from the Jasper rock in order to tumble polish them. I used a geological hammer (and I wore gloves and safety glasses while doing this), The pieces were sharp and a bit brittle.
The Jasper rock embedded in the track.
After being dug out and washed.
Not a good colour as this was taken inside, with poor lighting, but this gives an idea of the size of the Jasper rock.
A number of the Jasper fragments before being tumble polished.
After tumble polishing for about five weeks. Stone #1 is in the top row, far left.

Location of Waikaka at the bottom of the South Island (source: Google Maps):

Waikaka location

More on Jasper as a gemstone.

Other TumbleStone posts referring to “The Mains”: Maps as a Resource: New Zealand’s “Maps Past”, Part One; Maps as a Resource: New Zealand’s “Maps Past”, Part Two; Jasper Stones and Petrified Wood, Shepherd’s Creek, Waikaka; and “You run from the river, when it long ran over you…”

2) Stone #2 Granite or Basalt Porphyry, containing Feldspar Crystals

I found this stone at Riverton, Southland, in September 2018. This type of stone, while not numerous on Riverton beaches, is not rare and one is likely to be found within 10 to 15 minutes of searching. Its most obvious and interesting characteristic is the lighter-coloured feldspar crystals packed into the darker surrounding matrix. This indicates the stone is of volcanic origin, and is probably either basalt or granite. “Porphyry” is a term for the texture of an igneous rock consisting of large-grained crystals, such as feldspar or quartz, lodged in a fine-grained silicate rich matrix. These crystals formed within magma underground – this material then reached the earth’s surface and cooled relatively quickly, “trapping” the crystals in fine-grained rock. The crystals can vary in size, as shown in these three photos from the Riverton Museum “Te Hikoi” (these photos were taken with the permission of Museum staff in December 2016):

Riverton Museum (photo taken with permission)
Riverton Museum (photo taken with permission)
Riverton Museum (Photo taken with permission)

The Riverton Museum often has a display of local stones types, usually set up for children. The well-known geologist Hamish Campbell has been instrumental in putting this together. In 2017, the Museum developed a five-page pamphlet as a guide for children and families to collect nine different types of stones from the area between Riverton and Orepuki.

Riverton Museum Guide Children’s Rockhound Club Adventure p.4
Riverton Museum Guide Children’s Rockhound Club Adventure p.2

Rock Type 1 “Volcanic Rocks” would include Granite and Basalt Porphyry. Reference.com provides the following explanation of the differences between Granite and Basalt: Granite is an intrusive rock that is formed when magma cools inside the crust. This slow cooling gives time for crystals to grow, making it more coarsely grained than an extrusive rock, formed at the earth’s surface. Basalt, on the other hand, is an extrusive rock, with a smooth texture from rapid cooling, usually by water. Granite has a high silicon content; it is mostly made out of quartz, mica and feldspar. Basalt contains more calcium oxide, manganese oxide and iron compounds than granite. I am unable to exactly identify Stone #2. Granite stones can easily be found in the Riverton area (see Stone #4) but Stone #2 seems to be less coarsely grained than Granite.

Riverton’s Back Beach, on Foveaux Strait‎, a source of many interesting stones for polishing
Further to the west than the previous photo. The Back Beach lies just beyond the far-off point.
Riverton has many small beaches full of stones

Location of Riverton (source: Google Maps):

Riverton location

3) Stone #3 Unknown Variegated Green Stone

This stone, found at Riverton in February 2018, is darker green towards the thicker end, with the other end being a lighter green. When slowly rotated in the light, small specks of mica can be seen at the darker end. It is probably a metamorphic stone having been subject to significant heat and pressure at some stage. So I looked up metamorphic rocks in “A Photographic Guide to Rocks & Minerals in New Zealand” (2011), written by Nick Mortimer, Hamish Campbell and Margaret Low. Page 20 (see below) has a basic classification which led me to consider whether at least part of this stone could be “Hornfels”. Page 119 (also see below) mentions that Hornfels contains “small micas” and that some occur in the Bluff area, which is along the coast not far south-south-east of Riverton. 

“Photographic Guide to Rocks & Minerals of NZ” page 20
“Photographic Guide to Rocks & Minerals of NZ” page 119

Many of the stones on Riverton beaches are thought to have come down the Waiau River whose mouth is about 50 kms westwards.

Stones are often unique in their shape, size and patterns, and contain a range of elements, layers, intrusions and so on, which make them very difficult to identify with certainty. Chemical analysis is often needed. Stone #3 remains unidentified.

Stones #4 to #6 are described in Part Two.

South Island Stone Collecting Trip, Part Two – Riverton to Kaikoura

Continued from Part One.

Next stop was Riverton at the very bottom of the South Island, where we were based for the next three weeks – many thanks to Helen and Ray for the generous use of their holiday home. We collected many beach stones from the Riverton area and from nearby Gemstone Beach at Orepuki. The weather was cool and windy at times but not bad enough to discourage stone collecting. We met a handful of fellow stone collectors at Gemstone Beach and exchanged greetings and stories. We also spotted dolphins swimming off the beaches at Riverton.  

Riverton’s Back Beach, a great source of stones to polish
Fossicking for stones, Back Beach, Riverton
Crashing waves, Back Beach, Riverton
Hector’s dolphins, Riverton
Hector’s dolphins, Riverton
Along the coast from the Back Beach, Colac Bay hill in the background
A stormy day, Riverton coast
Gemstone Beach, near Orepuki
There were many stones exposed on Gemstone Beach

While based at Riverton, we took a day trip eastwards to Waipapa Point, Slope Point and Curio Bay, the latter being well known for its petrified forest that is uncovered at each low tide.

Waipapa Point lighthouse
Sea lion emerging from the surf at Waipapa Point
Waipapa Point
Slope Point is the southernmost part of the South Island
Rough seas at Slope Point
The stairs down to Curio Bay
Petrified fallen three at Curio Point becomes apparent as the tide recedes
Petrified tree stumps at Curio Bay
Petrified wood in the rocks at Curio Bay
Petrified tree stump, Curio Bay

One day we walked the Long Hilly Track through an old gold mining area near Orepuki. This included part of the 40 kilometre long Port’s water race, built in the 1870s and 1880s with the help of Chinese miners. We visited the Riverton Museum and found an excellent display on the Chinese goldminers. On a visit to the Southland Museum in Invercargill, we saw a natural history room that included a lot of local geological displays and information.

Round Hilly Track information panel.
Most of the track is through bush like this. It was a cold wet day.
About Port’s water race – 40 kms long
Port’s water race runs alongside the track for hundreds of metres
Ray starting at the bottom of part of Port’s water race
At times Port’s water race runs through short tunnels
Dams were constructed to feed water races for the gold mining.
An area behind one of the dams.
Information panel on the Chinese gold miners
A substantial Chinese settlement is now only bush
The southern-most Chinese settlement in the world

On the trip north, on the way home, we stopped off to see the Moeraki Boulders in North Otago. Some sea mist came down even though it was the middle of the day. The boulders are large spherical rocks, concretions that have been exposed through shoreline erosion from coastal cliffs. They consist of mud, fine silt and clay, cemented by calcite. The degree of cementation varies from being relatively weak in the interior of a boulder to quite hard at its outside rim. The boulders are cracked and eventually fall apart after having been exposed for some time. 

Tourists in the midday sea mist at the Moeraki Boulders
The Moeraki Boulders are a popular tourist attraction
Moeraki boulders on a misty midday
Moeraki boulders
The boulders originate in thecliffs behind the beach
The boulders eventually collapse

A day was spent at Birdlings Flat, near Christchurch, where we collected quite a few stones for polishing. We walked to the point where the stony beach meets the volcanic mass of Banks Peninsula, briefly disturbing a resting seal. The tide was low enough for us to look at the stones in the small bay past the seal. 

Birdlings Flat stones, among the best to polish
The seal that I stumbled upon
Going as far as possible at the Banks Peninsula end of Birdlings Flat

We also took the opportunity to visit Akaroa on Banks Peninsula where we saw thick clouds rolling slowly down over the hills.

Clouding rolling down the hills at Akaroa
Akaroa clouds

The road further up the east coast of the South Island, through Kaikoura, was open – it had to be rebuilt after the November 2016 magnitude 7.8 earthquake as well as additional landslides caused by recent storms. So we were able to view the earthquake aftermath, including the land that been raised out of the sea. Some parts of the coast were uplifted by six metres. One of the places we visited on the Kaikoura peninsula was Point Kean, well-known for its seal colony. A large area of many hectares/acres now lies dry where it once was under the sea. 

Large uplifted area, formerly under the sea, at Point Kean, Kaikoura
Point Kean, Kaikoura, land uplifted out of the sea by 2016 earthquake
Pont Kean, Kaikoura, looking back to the parking area
Seals are very relaxed about the people walking around at Point Kean, Kaikoura
Lounging seal, Point Kean, Kaikoura
Rain water pool on rocks previously under the sea
The sea looks a long way away
Off Point Kean, Kaikoura
Some interesting folded rocks have been exposed by the earthquake
Newly exposed folded rocks, Point Kean, Kaikoura

Then it was home across Cook Strait, a choppy but not uncomfortable crossing.

Leaving the South Island on a Cook Strait ferry
Passing another ferry in the middle of Cook Strait

 

The Seven Stages in Tumble Polishing Stones: The Selected 40 Stones

The first Post in this series described Stage One, Stone Collection. To illustrate the next six stages in the tumble polishing of stones, I decided to select 40 of the stones I had collected at Riverton in early November. I chose a range of sizes, colour and quality. The following are photos of all 40 stones, first of all how they appear dry and then how they appear wet. This demonstrates how wetness brings out colours and patterns much better.

Stones 1 to 5:

1st 4 dry1st 4 wet

It will be interesting to see how much of each stone is worn away throughout the tumbling process. Stone 1 (far left) is about 8 cms long and about 5 cms wide at its widest point (using the graph paper it is lying on in the “dry” pic above).  Stone 3 is about 6 cms long and 4.5 cms wide, while Stone 5 (far right) is just over 7 cms long and is 3 cms wide. I think that Stone 1 is of volcanic origin, as it has small specks in it that would have originally be gaseous pockets, and will turn out to be similar to another Riverton stone I polished recently (below). 

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Stone 2 is also probably volcanic in origin, having similar specks. Stone 4 looks like a conglomerate (which simply means it consists of small rounded stones cemented together in a fine-grained matrix). [As its surface became clearer after some tumbling, I decided Stone 4 is in fact a breccia, composed of angular fragments.] Stones 1, 2, 4 and 5 would be too big for a 3lb barrel.

Stones 6 to 10:

2nd 4 dry2nd 4 wet

These are progressively smaller, with Stone 6 (far left) being about 6 cms long and 4 cms wide. Stone 7 could be argillite (a kind of mudstone subjected to heat and pressure) or epidote (green coloured rock), Stone 9 is a breccia (which simply means it consists of broken fragments of very small stones) and Stone 10 is another conglomerate. 

Stones 11 to 15:

3rd 4 dry3rd 4 wet

The progression to smaller continues. Stone 14 (second from right) is a pink granite that is just over 5 cms long and is just under 4 cms wide at the top. Stone 12, a quartzite, demonstrates how wetness brings out the nature of a stone. Dry, it appears a bland white. Wet, patterns of colour in a strand-like formation become visible with a subtle depth being present. Stone 15, which could be argillite, has an interesting wavy band of white silica.  

Stones 16 to 20:

4th 4 dry4th 4 wet

Stones 18 and 19, both about 4 cms long, are potentially quite spectacular. Stone 18 has a number of different coloured bands. Stone 19 contains contrasting black and white sections, and it will be interesting to see if these erode or polish differently.

Stones 21 to 25:

5th 4 dry5th 4 wet

Stone 25 (far right) has some interesting bands that will be brought out by the tumble polishing, but Stone 22 (second from left) may turn out to be even more interesting. The white on the surface of Stone 23 (middle) may be worn away in the process it goes through, but there may be interesting patterns underneath.

Stones 26 to 30:

6th 4 dry6th 4 wet

Stone 26 (far left) is 3.5 cms long and just over 2.5 cms wide. Its two-toned character attracted my eye on the beach. White is a colour that always stands out on the beach too, Stone 27 being a white quartz with a couple of dark intrusions.

Stones 31 to 35:

7th 4 dry7th 4 wet

Stone 31 (left) may be part-jasper, and Stones 32 and 34 are probably varieties of jasper. Stone 33 has interesting reddish protuberance that caught my eye on the beach. Stone 35, white quartz, is 3 cms long and just under 2 cms wide. 

Stones 36 to 40:

8th 4 dry8th 4 wet

The smallest stone, Stone 40 (far right), jasper, is 2 cms by 1.5 cms. Up to 20% of a stone may be worn away by the tumbling process so not much may be left of this at the end. However, small stones are good in a tumbling barrel as they “carry” the grit and polish to the larger stones.   

I weighed the 40 stones on a set of scales I have in my stone tumbling shed. First placing the empty container on the scales, I moved the setting back to zero so that only the weight of the stones would be indicated = 1605 grams (3.5lbs).

a - weigh in

I will weigh the stones after each stage of tumbling to see how much of them is worn away. 

The next Post in this series describes Stage Two of tumble polishing, the 100 grit tumble.

Hard Won and Well Deserved! The Final Thesis Milestone

I supervised Charlotte’s Masters thesis, The Price of Pain: Studying Strategies Used by Women with Chronic Pain Disability to Sustain Worker Identity. As each chapter was completed, Charlotte chose a “milestone”, a polished stone to symbolise significant progress. This is the final milestone, chosen to signify the end of the journey. A fitting stone for a gem of a thesis!

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UPDATE

One year later, the “milestones” are still functioning as intended. Charlotte posted a comment and photo on Facebook:

“Someone came to replace my computer at work and noticed my milestones. They sit on my desk and are a reminder of how anything can be achieved one small step at a time. Still some of my favourite things and a wonderful reminder of each small step and the people who helped along the way.”

chstones

 

 

 

 

 

The Seven Stages in Tumble Polishing Stones: Stage One, Stone Collection, Riverton, 2-6 November 2017

NOTE: March 2021. Due to changes in the supply of grit and polish, plus a few other things, there are now six stages that I recommend instead of seven. The details are in UP-DATE OF “The Seven Stages in Tumble Polishing Stones” – One Less Stage. However, there are many useful practical suggestions in this original series so I have decided to leave it basically unchanged.

There are seven stages in the tumble polishing of stones. The first stage is acquiring the rough stones, stones of the right shape and condition and colour that show good promise for polishing. (Note that nearly all other accounts of tumble polishing don’t include stone collection as a stage.) Stage Two, for me, is tumbling the stones for about a week in 100 mesh silicon carbide grit, then tumbling them in a soap wash for a few hours. In Stage Three I repeat this process, using 220 mesh silicon carbide grit, while Stage Four is the same procedure with 320 silicon carbide grit. At this point, the stones should be shaped and smooth enough to begin actual polishing. I then use two polishing stages. Stage Five involves tumbling the stones in a tin oxide “Pre-Polish” powder (five microns in size) for three to five days, followed again by a few hours soap tumble. Stage Six is the “Pro-Polish” tumble, using tin oxide powder of one micron size, for at least one week. The final stage, Stage Seven, is a “burnishing” tumble for a week in borax. At every stage, stones are individually examined and may be set aside to repeat a stage or, more rarely, even skip a stage.

I emphasise that these seven stages describe what I normally do. However, I often start tumbling a newly collected smooth beach stone at Stage Four. Note that other tumble polishers often use different grits and polishes in different  ways. What I am describing is what I do and how I do it.

For me, Stage One, stone collection, usually involves spending time on beaches, head down, occasionally bending over to pick up a stone worthy of collection. The best way to decide if a stone is worth polishing is to view it wet, so I often walk along the sea edge where the waves roll in then die out as they wash over the sand and stones. I will often take a promising dry stone to the wave edge so it can be wettened to bring out its colour. If it is raining, all the better as I then do not need to keep on checking for the next big wave that may wash in and wet my feet.

I often wear gumboots but sometimes even those are overwhelmed by an unexpectedly larger or more energetic wave.

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Wringing out wet socks after a wave swept in further than expected and overwhelmed my gumboots. Bag of collected rocks beside me. This is at Orepuki (Gemstone Beach) near Riverton, 4 November 2017. Photo taken by Helen Hannah.

Clothes worn for stone collecting: usually warm clothes as beaches are often windy; gumboots or jandals depending on temperature; cap (if sunny) or woolen hat (if cold and cloudy); light waterproof coat and waterproof over-trousers if weather is wet. 

Equipment used for stone collecting: small backpack to carry drinking water, food, camera, plastic collecting bags, and collected stones.

Kinds of stones worth collecting: those with interesting colours and patterns; the smoother the better; the harder the better; the more slippery the better; with a minimum of cracks and pits and jagged edges; not too big (as the tumble barrels are small) and not too small (as the polishing process wears away a proportion of the stone). When wet, you can see a stone’s colours but the cracks and pits in it are not so easy to see. When dry, the cracks and pits can be more easily seen, but the stone will look dull.

I mainly collect beach stones and river stones. They have the advantage of being smoother and more easily identifiable than stones or rocks found anywhere else. They are easier to tumble polish because their jagged edges have already been worn off.

Some beaches have just a scattering of stones along the sand – it is still possible to find some very good specimens here as you stroll along.

 Other beaches have masses of stones. Sometimes a collector need just stand or sit there to find many good specimens.

Stone collecting means that you visit interesting and scenic places. During this trip to Riverton, I appreciated patterns on the sand at Henderson Bay, bird wildlife at the Back Beach, and the rising of a full moon over Taramea Bay.

Once the stones are collected, they need to be taken home. Sometimes, such as when I am travelling by aeroplane, that means putting them in a plastic container and then posting them. When I went to post some to my home in the North Island at a Post Shop in Gore, I was asked by the assistant, “Don’t they have any stones up there?” “Not like these, no,” I replied, and I showed her some polished ones I had in my pocket. She was amazed at their beauty and understood why I was doing such a strange thing as mailing what looked like ordinary everyday stones across the country. 

The next stage in tumble polishing happens at home after I unpack the collected stones or after the Postie has delivered those I earlier put in the mail. Stage Two involves tumbling rough stones in water and a low grade abrasive grit. In the next Post I will describe the Riverton stones selected to go through the stages of tumbling to illustrate this series. I will then look at their first tumble, in The Seven Stages in Tumble Polishing Stones: Stage Two, 100 Grit Tumble, 15-25 November 2017.

Field Trip to Southern Coast of South Island

I have recently returned from spending a week based in Riverton, visiting beaches in the area to collect stones for polishing. I brought home a total of 23 kgs of stones (14 kgs of which were posted) from six different beaches. The main collection sites were a handful of Riverton beaches as well as Orepuki, Bluff, and near Cosy Nook.  

Orepuki Beach
Looking down on the “Back Beach” at Riverton
The small beach next to Cosy Nook – a stream flows through the seaweed, revealing stones
Stirling Point, Bluff, just under the famous signpost
Glass on the Stirling Point beach at Bluff
The beach stones amidst boulders at Stirling Point, Bluff
23 kgs of collected stones

 

The Sound of Stones Tumbling on the Beach

“…The chatter of the pebbles as they tumble against one another… A beach is a strip of loose material at the water’s edge, a collection of sand and stones assembled, disassembled, and reassembled by the sea. On the geologic time scale, it is ephemeral. And for most stones, the beach is just the latest stop on a journey that began eons ago.” [Margaret Carruthers, “Beach Stones” (with photos by Josie Iselin), 2006, page 7]

I took some video clips during my recent visit looking for stones on Otago and Southland beaches. This movie (below) shows two of the stony Southland beaches on which I spent some time. The first one is the “Back Beach” as I know it, but it is also known more officially as Howells Point Beach, at Riverton. This beach is 90% stony and lies straight across Foveaux Strait from Stewart Island – usually a wild beach with powerful surf, the day I was there it was very calm (though the day was wet, cool and gray). The second beach featured on this movie is Tihaka Beach on Colac Bay, at the far eastern end of the Bay. This is a long stony beach, and the surf was a little stronger than at the Back Beach. So it was particularly at Tihaka Beach that you could hear the stones being tumbled as the waves came in and then receded. Stone tumblers mimic this action and intensify it.