The Borg cube like mass of interpenetrant crystals is made of calcite, just like stalactites and other formations in caves. Precipitated slowly out of calcium carbonate rich waters the crystals developed good transparency, but at the very end of their growth the waters started to contain an admixture of dissolved iron, which precipitated as small inclusions of the reddish orange iron oxide mineral haematite (see outlining their edges in a scene of near perfect beauty. The specimen comes from the Tsumeb mine in Namibia (see and measures 7 x11 x 5.7 cm.


Image credit: Exceptional Minerals