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. 

Author: tumblestoneblog

Retired Academic, male, living in the New Zealand countryside near Whanganui with his wife as well as Jasper the dog, Fluffy the cat, Dancer and Penny, the horses, and a shed half-full of stones. Email john.tumblestone@gmail.com. View all posts by tumblestoneblog