gerdtremmelite

During the first study of betpakdalite from Tsumeb (Schmetzer et al. 1984) an unknown arsenate containing zinc, aluminium and iron was detected. It was subsequently approved as a new mineral, IMA 1983-049a, and named for German chemist and mineral collector Dr Gerd Tremmel, who first recognised its potential as a new species (Schmetzer and Medenbach 1985). Type material is conserved at the Mineralogisch-Petrographisches Institut, Mineralien-sammlung, Universität Heidelberg, Germany (catalogue number 10’11’16) and at the Smithsonian in Washington D.C. (catalogue number 147360).

The type material (two specimens) consists of deeply oxidised sulphide ore from the second oxidation zone on which gerdtremmelite occurs in association with betpakdalite, hematite, kaolinite, powellite, quartz and scorodite. Gerdtremmelite occurs as spherulitic aggregates of minute tabular crystals (typically 3 µm across and 1 µm thick). Individual crystallites are transparent with an adamantine lustre but the spherulites vary in colour from yellowish-brown, through beige to dark brown (Schmetzer and Medenbach 1985).

Schluter et al. (1998) listed gerdtremmelite (and adamite) as components of the type assemblage for wilhelmkleinite. This is probably the "second discovery" of gerdtremmelite referred to by Gebhard (1999) in which he describes an association with blue aluminium-containing scorodite from the third oxidation zone.

adamite; betpakdalite-CaCa (?); hematite; kaolinite; powellite; quartz; scorodite; wilhelmkleinite