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Gypsum


Chemistry: CaSO4 2H2O
Size: 75 mm; (FOV for close-ups is 40 mm)
Owner: Malcolm Southwood
Photographer: Malcolm Southwood

Colourless to pale-green, composite and doubly terminated crystals of gypsum (to 70 mm) on a shard of matrix.  Powder XRD analysis has confirmed the presence of calcite, quartz and smithsonite in the non-sulphide portion of the matrix, while a second analysis of the sulphide component has confimed pyrite, sphalerite and tennantite.  There is a green micro-botryoidal crust of duftite (?) over part of the matrix (see Photograph 2) and, under magnification, it appears that microscopic inclusions of duftite (?) in the gypsum crystals probably account for their pale green colour.

Unfortunately the level of the mine from which this specimen was recovered is not recorded, although well-crystallised gypsum was most commonly encountered in the first oxidation zone.