sewardite

In June 1982, Dr Terry M. Seward (1940-2022) collected a specimen from 19 East, 31 Level in the second oxidation zone at Tsumeb. He suspected that an unidentified phase on this specimen was a new mineral based on its appearance, XRD pattern and a preliminary EDS-based composition. It would be 17 years, however, before a chance meeting with Dr Andrew Roberts of the Geological Survey of Canada led to its formal characterisation. IMA 2001-054 is the calcium-dominant analogue of carminite and was named sewardite in honour of its discoverer (Roberts et al. 2002). Type material is conserved at the Geological Survey of Canada, Ottawa (catalogue number 68095), the Natural History Museum, London (catalogue number BM.2001,36) and at Eidgenössische Technische Hochschule, Mineralogisch-Petrographische Sammlung, Zurich (catalogue number unknown).

Sewardite was described from a single specimen on which it occurred in a 3 cm sized vug where it was intergrown with a very dark green to black botryoidal mass which was shown to be an intimated intergrowth of ferrilotharmeyerite and another tsumcorite group phase that may be a Cu- and Zn-bearing variety of ferrilotharmeyerite or possibly a Zn-dominant analogue of lukrahnite.

On the type specimen sewardite occurs as dark-red, platy to compact, anhedral to subhedral masses (to 0.3 mm) that are randomly scattered through the dark green to black matrix (Roberts et al. 2002). There are no obvious crystal forms and twinning was not observed. However, sewardite closely resembles carminite and visual distinction of the two minerals is virtually impossible. The colour of sewardite is dark red in masses but a much lighter orange on the thin edges of crystal fragments.

Sewardite has been verified as occurring with scorodite on a specimen formerly in the collection of Shields Flynn. Images and analytical data are available on the RRUFF database at (https://rruff.info/sewardite/display=default/R141206; accessed November 2015).

betpakdalite-CaMg; beudantite; ferrilotharmeyerite; germanite; lukrahnite; scorodite