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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:
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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