This is an extremely rare and significant specimen of the silver selenide mineral Naumannite from its Type Locality in the Tilkerode Mining District (Harz), Mansfeld, Saxony-Anhalt, Germany. Naumannite was first described in 1828 and although the accompanying historic handwritten labels are old, they don't appear to be quite that early. The latest label, that which refers to Senator F.J. Kessler (1805-1889), is from the institution where his collection was donated in 1909. The very neat handwritten label is probably Kessler's own label. As a large miniature it is a great size piece for this rarity, showing the classic iron oxide matrix and white Calcite veins containing dark grey Naumannite and Clausthalite. It is from the superb systematic collection assembled by the brothers Martin and Michael Günther (1951-2007 & 1956-2021).
