River Flow CAFFAS 2 – Water surface texture in the fast flowing shallow chalk River Cerne just above the sluice at Forston Farm in Dorset, England, October 2017.
Yes, I can see that – black volcanic glass which is opaque en masse but translucent in thin section. It is interesting that this stretch of water can look so very different at other times of the year. When the water is shallower and the light is brighter, the coloured stones on the river bed make the water look like sparkling jewels.
Jessica's Nature Blog 
Reminds me of Obsidian.
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Yes, I can see that – black volcanic glass which is opaque en masse but translucent in thin section. It is interesting that this stretch of water can look so very different at other times of the year. When the water is shallower and the light is brighter, the coloured stones on the river bed make the water look like sparkling jewels.
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