Some grass green crystals and crystal aggregates of the extremely rare mineral guildite in a capsule from the type and only known locality worldwide: United Verde Copper Mine, Jerome, Arizona, United States of America. — Photo: David Hospital · CC BY-SA 4.0
Guildite
Guildite is an IMA-recognized mineral species in the sulfate class, with the chemical formula CuFe³⁺(SO₄)₂(OH)·4H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/m).
Key properties: Mohs hardness 2.5; specific gravity 2.69–2.72; Pale canary-yellow streak; Vitreous luster; optically biaxial.
IMA symbol Gdi, grandfathered status — known before the IMA’s founding, named in 1928.
A rare secondary mineral formed in mine workings by burning pyritic ores.
It is found associated with Coquimbite, ransomite.
The mineral was named to honor Professor Frank Nelson Guild (1870–1939), American mineralogist and economic geologist, University of Arizona, Tucson, Arizona, USA.