Kusachiite

Kusachiite is an extremely rare binary copper(II) and bismuth(III) oxide with a chemical formula CuBi2O4. This sample belongs from the Type Locality: the well-known Fuka mine in Japan. This sample is rich in radial aggregates of kusachiite crystals, with a deep brown to black colour and contasting on the matrix. They are accompanied by calcite, quartz and other species like cahnite or bismite. We have carried out some SEM-EDS analysis and Raman. With these spectroscopical techniques we have confirmed the presence of the species. — Photo: Joan Rosell , from rosellminerals.com · CC BY-SA 4.0

Kusachiite

Kusachiite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Cu²⁺Bi³⁺₂O₄.

It crystallizes in the tetragonal crystal system (space group P4/ncc). It is a member of the Trippkeite structural group.

Key properties: Mohs hardness 4.5; specific gravity 8.5; Black streak; Metallic luster; optically uniaxial.

IMA symbol Kus, IMA status: approved, named in 1992.

On calcite crystals in a calcite vein between gehlenite-spurrite skarn and limestone; thought to be of low-temperature hydrothermal origin.

It is found associated with Henmilite, sillénite, bakerite, tenorite, bultfonteinite, apophyllite, cuspidine, thaumasite.

The mineral was named to honor Dr. Isao Kusachi (1942–), Professor of Mineralogy, Okayama University, Okayama, Japan, for his work on skarn minerals of the Fuka area.