Month: April 2020

Stay-at-Home Day Twenty-Six, Monday 20 April 2020: Stone Twenty-Six

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Stone Twenty-Four.
Stone Twenty-Three.
Stone Twenty-Two.
Stone Twenty-One.

Stone Twenty-Six is a polished banded agate stone from Birdlings Flat. I found it over a year ago and, after it had been stored for a few months, finished polishing it last month. It carries scratches and other damage from being smashed against rocks and stones by powerful waves. In order to keep the stone at a decent size, all of the bumps and nicks have not been smoothed away in the tumbler.

Stone Twenty-Six.
Stone Twenty-Six.
Other side of Stone Twenty-Six.
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The bands become clearer when the stone is viewed edge-on, and when it is held up to light.

Edge view of Stone Twenty-Six.
Edge view of Stone Twenty-Six.
Held up to the light (inside), edge view of Stone Twenty-Six.

Just as hydrogrossular garnets are the most sought-after stones on Gemstone Beach, so agates are the most sought-after stones on Birdlings Flat. 

Stone Twenty-Six up close.
Stone Twenty-Six up close. The small cresent shapes are probably the result of percussive blows from other stones.
Stone Twenty-Six up close.

Agate is a cryptocystalline form of quartz that has precipitated from silica-bearing groundwater in rock cracks and cavities. It is similar to the way “sinter” is preciptated from geothermal hot waters flowing from geysers and hot springs. We are more used to agates as polished slabs of colourful semi-concentric patterns, the colour caused by various minerals like iron and manganese. Malcolm Luxton has published an amazing book, “Agates of New Zealand” (2015), which is packed full of information on and photos of such agates as found in New Zealand (available from the likes of Wheelers).

From Malcolm Luxton’s “Agates of NZ” (2015), p. 91.
From Malcolm Luxton’s “Agates of NZ” (2015), p. 192.
From Malcolm Luxton’s “Agates of NZ” (2015), p. 254.
From Malcolm Luxton’s “Agates of NZ” (2015), p. 144.
From Malcolm Luxton’s “Agates of NZ” (2015), p. 230.

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 kilometres 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). Vince Burke’s Birdlings Flat Gemstone and Fossil Museum contains a number of magnificent agate slabs from especially Canterbury. And the Museum also contains many specimens of the smaller plainer agates to be found at Birdlings Flat.

Colourful agate slabs, Birdlings Flat Gemstone and Fossil Museum.
Agate stones, Birdlings Flat Gemstone and Fossil Museum.
Colourful agate slabs, Birdlings Flat Gemstone and Fossil Museum.
Agate stones, Birdlings Flat Gemstone and Fossil Museum.
Agate stones, Birdlings Flat Gemstone and Fossil Museum.

These small agate stones, like Stone Twenty-Six, are the remnants of the breaking up of the colourful slab agates, coming from the un-coloured surrounding rock. They are often very plain and only sometimes have bands (layered precipitated material).

Holding Stone Twenty-Six up to the light, it is possible to see that agate is much more translucent than hydrogrossular. 

Stone Twenty-Six held up to the light, outside.
Stone Twenty-Six held up to the light, inside.

And the patterns revealed in the light, from the history of the stone’s formation and battering by the waves against other stones, are utterly fascinating.

Stone Twenty-Six.
Stone Twenty-Six held up to the light – detail, with colour saturation.
Stone Twenty-Six held up to the light – detail.
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The next Post in this Series is Stay-at-Home Day Twenty-Seven, Tuesday 21 April 2020: Stone Twenty-Seven. The first Post is Stay-at-Home Day One, Thursday 26 March 2020: Stone One. 

Stay-at-Home Day Twenty-Five, Sunday 19 April 2020: Stone Twenty-Five

Stone Twenty-Four.
Stone Twenty-Three.
Stone Twenty-Two.
Stone Twenty-One.
Stone Twenty.

Stone Twenty-Five was found on Gemstone Beach:

Stone Twenty-Five.
One side of Stone Twenty-Five.
Stone Twenty-Five.
Edge of Stone Twenty-Five.
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It has polished very well, which makes it difficult to photograph without a lot of reflection. This is especially so for the side which is more raised. I tried photographing it inside on a light coloured surface, but without much improvement.

One side of Stone Twenty-Five, photo taken inside.
Stone Twenty-Five.

I am unable to identify this stone. It looks to me to be possibly along the gneiss-schist spectrum, but this is a pure guess with little to support it.

Stone Twenty-Five in detail.
Stone Twenty-Five in detail.
Stone Twenty-Five in detail.
Stone Twenty-Five in detail.
Stone Twenty-Five in detail.
Stone Twenty-Five.
Stone Twenty-Five in detail.
Stone Twenty-Five in detail.

Gneiss and schist are common and widely distributed types of metamorphic rock, formed by high temperature and high-pressure metamorphic processes acting on  igneous or sedimentary rocks. Gneiss is coarser grained than schist because it forms at higher temperatures (over 450 degrees C) and pressures than schist.

The next Post in this Series is Stay-at-Home Day Twenty-Six, Monday 20 April 2020: Stone Twenty-Six. The first Post is Stay-at-Home Day One, Thursday 26 March 2020: Stone One. 

Stay-at-Home Day Twenty-Four, Saturday 18 April 2020: Stone Twenty-Four

Stone Twenty-Three.
Stone Twenty-Two.
Stone Twenty-One.
Stone Twenty.
Stone Nineteen.

Stone Twenty-Four is a banded argillite, a mudstone:

Stone Twenty-Four.
One side of Stone Twenty-Four.
Stone Twenty-Four.
Stone Twenty-Four.

The bands are compressed strata of muddy sediment laid down under the sea, millions of years ago.

Stone Twenty-Four.
Stone Twenty-Four.
Stone Twenty-Four.
Stone Twenty-Four.

It’s possible to find these stones at Gemstone Beach and also Riverton. This one comes from Gemstone Beach. The grey colour, and dark and light bands, mean that these stones stand out and catch the eye. They are fine-grained and smooth, and polish well.

Stone Twenty-Four close up.
Stone Twenty-Four close up.
Stone Twenty-Four close up.
Stone Twenty-Four close up.
Stone Twenty-Four close up.
Stone Twenty-Four close up.
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The next Post in this Series is Stay-at-Home Day Twenty-Five, Sunday 19 April 2020: Stone Twenty-Five. The first Post is Stay-at-Home Day One, Thursday 26 March 2020: Stone One. 

Stay-at-Home Day Twenty-Three, Friday 17 April 2020: Stone Twenty-Three

The same close-up with more “saturation”.
Stone Twenty-One up-close.
Stone Twenty close-up.
Stone Nineteen.
Stone Eighteen.

Stone Twenty-Three comes from Birdlings Flat in Canterbury and is probably volcanic in origin (could be rhyolite). There are small crystals of different colours within a light brown matrix. Some of the white crystals appear to be quartz. Light coloured  igneous rocks like this one are usually silica rich.  

Stone Twenty-Three.
Stone Twenty-Three.
Other side of Stone Twenty-Three.
Stone Twenty-Three.

Stones like this usually don’t tumble successfully as some of the small fragments within them tend to come loose. However, they are colourful stones with interesting inclusions and I am always hopeful of a good outcome.

Stone Twenty-Three.
Stone Twenty-Three.
Stone Twenty-Three.
Stone Twenty-Three.
Stone Twenty-Three.
Stone Twenty-Three.
Stone Twenty-Three.

The next Post in this Series is Stay-at-Home Day Twenty-Four, Saturday 18 April 2020: Stone Twenty-Four. The first Post is Stay-at-Home Day One, Thursday 26 March 2020: Stone One. 

Stay-at-Home Week Three, Stone of the Week

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18 – Claimed
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20
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The bowl of Stones of the Day in my home office is fuller now, having a total of 21 polished stones in it.

As for Weeks One and Two, my small Facebook community voted on a Stone of the Week for Week Three. “Which stone is your favourite?” I asked, regarding Stones Fifteen to Twenty-One. Stone Eighteen attracted the most support. 

18 – Claimed
Stone Eighteen.
Stone Eighteen.

The next Post in this Series is Stay-at-Home Day Twenty-Two, Thursday 16 April 2020: Stone Twenty-Two. The first Post is Stay-at-Home Day One, Thursday 26 March 2020: Stone One. 

Stay-at-Home Day Twenty-Two, Thursday 16 April 2020: Stone Twenty-Two

Stone Twenty-One.
Stone Twenty.
Stone Nineteen.
Stone Eighteen.
Stone Seventeen.

Stone Twenty-Two is a hydrogrossular garnet found on Gemstone Beach last month, polished last week. Stone Eleven was the classic gooseberry-green hydrogrossular whereas this stone is a light grey colour with white clouds within it.

Stone Twenty-Two.
Stone Twenty-Two.
Other side of Stone Twenty-Two.
A third side of Stone Twenty-Two.
Stone Twenty-Two from another angle.
Stone Twenty-Two.

The “white clouds” up close are reminiscent of ice floes in a fog-covered freezing sea.

Stone Twenty-Two up close.
Stone Twenty-Two up close.
Stone Twenty-Two up close.
Stone Twenty-Two up close.
The same close-up with more “saturation”.
Stone Twenty-Two up close.
Stone Twenty-Two up close.
Stone Twenty-Two up close.
Stone Twenty-Two up close.
Stone Twenty-Two up close.

Riverton Museum Te Hikoi has a collection of hydrogrossular pebbles that display the range of colours and types.

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Hydrogrossular garnets in Riverton Museum. Photo taken by me in December 2016, with permission of Museum staff.

The next Post in this Series is Stay-at-Home Day Twenty-Three, Friday 17 April 2020: Stone Twenty-Three. The first Post is Stay-at-Home Day One, Thursday 26 March 2020: Stone One. 

Stay-at-Home Day Twenty-One, Wednesday 15 April 2020: Stone Twenty-One

Stone Twenty.
Stone Nineteen.
Stone Eighteen.
Stone Seventeen.
Stone Sixteen.

At the end of Week Three, Stone Twenty-One is another fossil worm cast stone. This stone is a medium-green argillite, the trace fossils being light green. Such a colour combination is the most common for worm cast stones at Gemstone Beach and Riverton. Argillite is a hardened, slightly recrystallised, mudstone. The darker in colour it is, the finer grained it is. 

Stone Twenty-One.
Stone Twenty-One.
Stone Twenty-One.
One side of Stone Twenty-One.

Some of the traces on this stone are chevron shaped.

Stone Twenty-One, chevron shaped trace fossil on bottom of stone
Stone Twenty-One, semi-chevron shaped trace fossil.
Stone Twenty-One up-close.
Stone Twenty-One up-close.

What is unusual about this stone is that some of the fossil casts or trails appear elongated, maybe stretched from the pressures that turned sediment to rock over thousands of years. 

Stone Twenty-One, elongated trace shape.
Stone Twenty-One, elongated trace shape.
Stone Twenty-One, elongated trace shape.

This is the fourth worm cast stone featured in Week Three of Stay-at-Home:

One side of Stone Twenty-One.
Stone Nineteen.
Stone Seventeen.
Stone Fifteen.

The next Post in this Series is Stay-at-Home Week Three, Stone of the Week.

Stay-at-Home Day Twenty, Tuesday 14 April 2020: Stone Twenty

Stone Nineteen.
Stone Eighteen.
Stone Seventeen.
Stone Sixteen.
Stone Fifteen.

A Birdlings Flat stone, collected over a year ago, polished last month:

Stone Twenty.
Stone Twenty.
Stone Twenty.
Other side of Stone Twenty.

This again is a quartzite, like Stones Two and Nine. There are patches and flows of golden-yellow within the stone.

Stone Twenty close-up.
Stone Twenty close-up.
Stone Twenty close-up.
Stone Twenty close-up.
Stone Twenty close-up.
Stone Twenty close-up.

I have picked up and polished a  number of these yellow quartzites on Birdlings Flat – it is even possible to find quite large stones of it, much too large to tumble polish or even to take home.

Larger yellow quartzite found on Birdlings Flat, February 2020.
Larger yellow quartzite found on Birdlings Flat, February 2020.
Range of yellow quartzites found on Birdlings Flat in 2016.
Found on Birdlings Flat in May 2016.

What fascinates me about these stones are the “clouds” or “curtains” of golden-yellow that are situated through them – the photos fail to do justice to the 3-D nature of these clouds and curtains. There are depths clearly visible in these stones – you can see into them.

The next Post in this Series is Stay-at-Home Day Twenty-One, Wednesday 15 April 2020: Stone Twenty-One.

Stay-at-Home Day Nineteen, Monday 13 April 2020: Stone Nineteen

Stone Eighteen.
Stone Seventeen.
Stone Sixteen.
Stone Fifteen.
Stone Fourteen.

Stone Nineteen is the third fossilised worm cast stone this week. But it is a very rare black one. I found it on Gemstone Beach. 

Stone Nineteen.
Stone Nineteen.
Stone Nineteen.
Other side of Stone Nineteen.

The fossil traces on Stone Nineteen are different from those on Stones Fifteen and Seventeen, being less linear. In at least three instances, we are viewing the worm cast or trail from above, as it were, as it emerges from the depths of the stone.

Stone Nineteen.
Stone Nineteen detail.
Stone Nineteen detail.
Stone Nineteen detail.
Stone Nineteen.

Stones Nineteen, Seventeen and Fifteen, three different fossil worm cast stones:

Stone Nineteen.
Stone Seventeen.
Stone Fifteen.

The next Post in this Series is Stay-at-Home Day Twenty, Tuesday 14 April 2020: Stone Twenty.

Stay-at-Home Day Eighteen, Easter Sunday 12 April 2020: Stone Eighteen

Stone Seventeen.
Stone Sixteen.
Stone Fifteen.
Stone Fourteen.
Stone Thirteen.

Stone Eighteen is from Gemstone Beach:

Stone Eighteen.
Stone Eighteen.
One side of Stone Eighteen.
One side of Stone Eighteen.

I saw quite a few stones like this one on beaches in the south of the South Island long before I decided to try and polish one. Initially they seemed to be just rusty white stones, often with rough chipped surfaces. But when I noticed a few with reddish-brown or black veins, I thought I would tumble a few and see how they turned out. I discovered they had very interesting patterns that reminded me of a type of marble that I fancy sometimes I have seen in buildings in Europe (maybe on tv).

Stone Eighteen.
Stone Eighteen detail.
Stone Eighteen.
Stone Eighteen detail.

I am pretty sure these are not marble but I have come to think of them as “South Coast marble type” stones. They come in predominantly white or yellow, with black or rust-coloured veins. This type of stone can be difficult to polish and often has patches of roughness or tiny holes that can be difficult to remove.

Other “South Coast marble type” polished stones.
Other “South Coast marble type” polished stones.
An area on the side of Stone Eighteen that did not smooth and polish.

The next Post in this Series is Stay-at-Home Day Nineteen, Monday 13 April 2020: Stone Nineteen.