MARTIN LAND / SCIENCE PHOTO LIBRARY MARTIN LAND / SCIENCE PHOTO LIBRARY
Dog's tooth calcite crystals. The dark grey substrate is sphalerite (zinc iron sulphide). Calcite (calcium carbonate) is a typical sedimentary mineral which usually occurs in large masses. Limestones, marbles, alabasters and stalactites & stalagmites are composed of calcite. Calcite crystals are colourless or white. Large, clear crystals were formerly used to make polarizing prisms (Nichol prisms) for microscopes.
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