gerdtremmelite (w. scorodite and powellite)

A breccia of flat siliceous clasts, encrusted with hematite and quartz. Translucent blue crystals of scorodite (to 10 mm) are sparsely distributed on the breccia, with fans (to 2 mm) of platy, straw-yellow powellite crystals and a rich but localised encrustation comprising intergrown spherules (individually to 0.3 mm) of brown gerdtremmelite (Exhibit 2). A white fibrous mineral, occasionally forming small aggregtes, is also present; it has not been analysed but, based on the original description of gerdtremmelite (Schmetzer and Medenbach 1985), it is possibly kaolinite (?).

The specimen is from the Pinch Collection and Pinch's label (Exhibit 3) describes it as "original type material" but with no further information on provenance. Pinch's mention of "pyrophyllite" almost cerrtainly refers to the white fibrous mineral which, based on the original description of gerdtremmelite, is more likely to be kaolinite (?).

The paragenesis is definitively from the second oxidation zone.

hematite; kaolinite (?); powellite; quartz; scorodite