Euhedral quartz ‘potato stone”, devon, uk – natural euhedral quartz “potato stone” from devon, uk

Description

SIZE (Picture scale cube=1cm):  30 x 30 x 17mm (1.18 x 1.18 x 0.67 inches)

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Euhedral Quartz – “Potato Stone”, Triassic, Sidmouth, Devon, UK.

Quartz replacement of a Sabkha Anydrite Nodule, like those of a modern Sabkha.

The type of precursors are found today in the Dukhan Sabkha of Qatar. Modern desert sabkhas are often “Khaki” (light brown) in colour. The hydrated iron oxide (goethite) is converted by heat under burial to the reddish colour. The Trisssic mudstone probably was a filthy brown mud, but now looks quite attractive as hard mudstone. The calcium sulphate of the nodule has been partially replaced by euhedral quartz crystals growing in from the margin (pH controlled). Residual secondary gypsum, has very recently been dissolved away to leave a hollow centre.