willemite (on dolomite and smithsonite)

A matrix of iron-stained dolostone hosts a vug lined with an intergrown mixture of dolomite and smithsonite; both are white and visually indistinguishable, but both are XRD-confirmed (Exhibit 3). The surface of the dolomite / smithsonite is decorated with bright, apple-green willemite crystals (to 3 mm) which have formed preferentially over fractures in the underlying carbonate (Exhibit 2). The colour of the willemite is unusual for Tsumeb. Note also the twinned willemite crystal at upper left of the close-up image and sparse, tiny spherules of a blue-green mineral - possibly rosasite (?) (Exhibit 2).

The specimen is from the collection of A. Glen Smith, which was donated to National Museum of Australia in 1982; it is now housed at Geoscience Australia, in Canberra.

The location in the mine is not recorded.

dolomite; rosasite (?); smithsonite