Dolomite ps. after Calcite with Malachite

Unknown Owner

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This miniature specimen is a Tsumeb classic, but rather than being a straight forward replacement of Dolomite after Calcite, the cream coloured Dolomite has created a porous, open texture, as it has substituted for the Calcite. This is presumably similar to the process of metasomatism in limestone when it is dolomitized - the change in volume as some of the calcium atoms are replaced by magnesium creates cavities. The original rhombic form of Calcite can still be seen very well on the outer surface, and underneath the internal casts can be seen. This is really a combination of Dolomite pseudomorphing Calcite crystals, but the internal casts are also epimorphs. Minor spots of green Malachite are sparsely scattered upon the outer surface, adding a little additional colour. Ex John Schneider collection, no. 1709.