Grandreefite
A rare secondary lead sulfate-fluoride discovered in 1989 at Arizona's Grand Reef mine.
Intro adapted from Wikipedia (CC BY-SA).
Grandreefite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Pb₂(SO₄)F₂.
It crystallizes in the monoclinic crystal system (space group A2/a).
Key properties: Mohs hardness 2.5; specific gravity 7; White streak; Subadamantine luster; refractive index 1.88; optically biaxial.
IMA symbol Grf, IMA status: approved, named in 1988.
Found as a rare secondary mineral in isolated vugs in the oxidized portions of a breccia-hosted hydrothermal Cu–Pb–Ag deposit.
It is found associated with Pseudograndreefite, laurelite, aravaipaite, galena, fluorite, anglesite.
The name refers to the Grand Reef mine, Arizona, USA.