Cornwallite

Maucher (1908a,b) provisionally identified "erinite" as a grey-green crust on malachite, but was unable to isolate a sample of sufficient purity for analytical confirmation. Unfortunately, this record is ambiguous because "erinite" is a pseudonym of both chalcophyllite (Beudant 1832, Des Cloizeaux 1845; see Palache et al. 1951) and cornwallite (Haidinger 1828; see Palache et al. 1951).

Bartelke (1976) cautiously interpreted Maucher’s (1908a) "erinite" as cornwallite, which seems reasonable, given that Maucher’s description (habit and colour) appears more consistent with cornwallite than with chalcophyllite. (It is noted, however, that Pinch and Wilson (1977) took the opposite view, listing "Chalcophyllite ("erinite")" as occurring at Tsumeb on the basis of Maucher’s (1908a) commentary.)

Gebhard (1999) reported that the only known specimen of cornwallite (with malachite and bayldonite, on quartz), is held at the Hamburg Museum, in Germany. A portion of this specimen, supplied by Gebhard, is now in the Feinglos Collection at Harvard University (MGMH 2022.4.8098). The cornwallite occurs as sparse green microcrystalline spherules (to 0.5 mm) on milky-white quartz which is highlighted by dustings of an unidentified green arsenate – possibly also cornwallite (?) or possibly bayldonite as suggested by Gebhard.