Cronstedtite

cronstedtite

clinochlore

siderite

fayalite

Images

Formula:(Fe2+,Fe3+)3(Si,Fe3+)2O5(OH)4
Phyllosilicate (sheet silicate) serpentine subgroup
Formula: Fe3Si2O5(OH)4
Crystal System: Trigonal
Specific gravity: 3.34 to 3.35 measured
Common impurities: Al,Ca
Hardness: 3½
Streak: Dark olive green
Colour: Black, dark brown-black, green-black
Environments:

Hydrothermal environments

Cronstedtite is a low temperature hydrothermal product in ore veins, commonly associated with clinochlore, pyrite, quartz, siderite and sphalerite.

Localities

At the Rare Metals Mine, Aquarius Mountains, Mohave County, Arizona, USA, chevkinite has been found associated with titanite, monazite, apatite, cronstedtite and quartz (AM 31.582–588).

Alteration

fayalite, H2O and O2 to cronstedtite and magnetite
6Fe2+2(SiO4) + 6H2O + ½O2 = 3Fe3Si2O5(OH)4 + Fe2+Fe3+2O4
(DHZ 1A p262)

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