Thaumasite

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From the Kalahari Manganese Fields, a very rare gem crystal of thaumasite -- a strange mineral with an extremely unusual chemical composition. In fact, the name is derived from the Greek thaumasion, which means "surprising." It is sometimes classified as a silicate due to its silicon content, but there is an argument to be made for its classification as a carbonate as well. However it does belong to a predominantly sulfate mineral group, the Ettringite Group, and its properties seem more in line with its inclusion into the sulfate class. It is quite rare in gem crystals, and they are inevitably small, as this one is. This is a complete, very gemmy crystal, finely terminated, with a little sidecar crystal.