A mass of radiating black crystals of deerite on and on matrix. JSS specimen and photo. From: Laytonville Quarry, Laytonville, Coastal Range, Mendocino Co., California, USA. — Photo: John Sobolewski · CC BY 3.0
Deerite
Deerite is an IMA-recognized mineral species in the silicate class, with the chemical formula Fe²⁺₆Fe³⁺₃(Si₆O₁₇)O₃(OH)₅.
It crystallizes in the monoclinic crystal system (space group P2_1/a).
Key properties: specific gravity 3.837; optically biaxial.
IMA symbol Dee, IMA status: approved, named in 1964.
Found in meta-ironstones and Cu-Fe sulfide deposits, in blueschist facies metasediments formed at high pressure and low temperature.
It is found associated with Howieite, zussmanite, stilpnomelane, spessartine, riebeckite, quartz, aegirine, grunerite, aragonite, manganoan siderite.
The mineral was named to honor Professor William Alexander Deer (1910{), mineralogist-petrologist, Cambridge University, Cambridge, England.