ARSENTSUMEBITE with TSUMEBITE with MIMETITE

SPECIMEN DESCRIPTION

A miniature piece of cherty matrix is coated on one side with a thin film of green microcrystalline Arsentsumebite-Tsumebite which is itself studded with larger, pale yellow to white, prismatic Mimetite crystals. The Arsentsumebite and Tsumebite form microscopic casts, or epimorphs, after an earlier unidentified mineral. Arsentsumebite and Tsumebite form a solid-solution series between arsenate and phosphate, the latter (Tsumebite) being by far the rarer. The slightly paler green colour and more glassy appearance of the Arsentsumebite/Tsumebite microcrystals is more akin to the Tsumebite end of the series. Some of the small hexagonal prisms of Mimetite are quite glassy in appearance and many show colour zonation. From the Type Locality of Arsentsumebite and Tsumebite which, in case you haven't guessed from their names, is Tsumeb mine in Namibia.