Tufa
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Tufa is a variety of limestone formed when carbonate minerals precipitate out of water in unheated rivers or lakes. Geothermally heated hot springs sometimes produce similar carbonate deposits, which
Tufa columns at Mono Lake, California
Barrage Tufa at Cwm Nash, South Wales
Rubaksa tufa plug, after drying of the river, in Ethiopia
Tufa deposits at Huanglong, Sichuan, China
Ikaite
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Ikaite is the mineral name for the hexahydrate of calcium carbonate, CaCO3·6H2O. Ikaite tends to form very steep or spiky pyramidal crystals, often radially arranged, of varied sizes from thumbnail si
Glendonite (calcite pseudomorph after ikaite)