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Genus of rock found in Somerset

Gypsum rockQ. Can someone please advise us as to the genus of the attached rock which was discovered in a field near the coastal resort of Minehead, in Somerset?

The top, white area, has steadily eroded over the past few months, to a point now where the rock is now purely the red substance...
Any help on this matter is greatly appreciated, as its existence has caused widespread confusion amongst the non-geologist community.

From Jim Arnott (October 2013)

Reply by Dr Ted Nield

This is a gypsum nodule from the Triassic, which crops out along the Severn on both English and Welsh sides.  Best place to see it in Somerset is probably Aust cliff, or, in Wales – Penarth in the Vale of Glamorgan. 

Gypsum – calcium sulphate, in this case stained red by iron oxide, is an evaporite mineral, reflecting the arid climate that prevailed in the UK during the Triassic, which was the time of maximum compaction of the previous Supercontinent, Pangaea.  Britain lay in the midst of this huge landmass, just a little north of the equator at that time, but nearly all of Pangaea was desert, and stretched from pole to pole.  For that reason Triassic rocks, almost everywhere they survive, show signs of desert origins.