Crystal grown from wall to wall at the bottom of a geode of cuprite. Locality: Cerro Minado Mines, Cuesta Alta, Huércal-Overa, Almería, Andalusia, Spain. Photo 1 mm width. Collection and photo of Angel Romero — Photo: Ángel Romero Escobar · CC0
Gerhardtite
The rare mineral form of basic copper nitrate — a green oxidation-zone mineral named for chemist Charles Gerhardt.
Intro adapted from Wikipedia (CC BY-SA).
Gerhardtite is an IMA-recognized mineral species in the nitrate class, with the chemical formula Cu₂(NO₃)(OH)₃.
It crystallizes in the orthorhombic crystal system (space group P2_12_12_1).
Key properties: Mohs hardness 2; specific gravity 3.4–3.43; Pale green streak; [Vitreous.] luster; optically biaxial.
IMA symbol Ghd, grandfathered status — known before the IMA’s founding, named in 1885.
Found as a rare secondary mineral in oxidized portions of copper deposits.
It is found associated with Cuprite, malachite, atacamite, miersite, brochantite, pseudomalachite, buttgenbachite, likasite, connellite, claringbullite.
The mineral was named to honor Charles Frederic Gerhardt (1816–1856), American chemist who first prepared the artificial compound.