Ikaite

Ikaite is the mineral name for the hexahydrate of calcium carbonate, CaCO3ยท6H2O. Ikaite tends to form very steep or spiky pyramidal crystals, often radially arranged, of varied sizes from thumbnail size aggregates to gigantic salient spurs. It is only found in a metastable state, and decomposes rapidly by losing most of its water content once rem...
Found on http://en.wikipedia.org/wiki/Ikaite
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