Cronstedtite

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Cronstedtite
Cronstedite France.jpg
Cronstedtite - Salsigne Mine - France
General
CategorySilicate minerals
Formula
(repeating unit)
Fe2+2Fe3+(Si,Fe3+O5)(OH)4
Strunz classification9.ED.15
Crystal systemTrigonal
Crystal classDitrigonal pyramidal (3m)
(same H-M symbol)
Space groupP31m
Unit cella = 5.486 Å,
c = 7.095 Å; Z = 1[1]
Identification
ColorBlack, dark brown-black, green-black
CleavagePerfect on {001}
TenacityElastic
LusterSub-Metallic
StreakDark olive green
DiaphaneityTranslucent
Specific gravity3.34 - 3.35
Optical propertiesBiaxial (-)
Refractive indexnα = 1.720 nβ = 1.800 nγ = 1.800
Birefringenceδ = 0.080
PleochroismVisible
Dispersionr < v moderate
References[1][2][3]

Cronstedtite is a complex iron silicate mineral belonging to the serpentine group of minerals. It has a formula of Fe2+2Fe3+(Si,Fe3+O5)(OH)4.

It was discovered in 1821 and named in honor of Swedish mineralogist Axel Fredrik Cronstedt (1722–1765). It has been found in Bohemia in the Czech Republic and in Cornwall, England.

Cronstedtite is a major constituent of CM chondrites, a carbonaceous chondrite group exhibiting varying degrees of aqueous alteration. Cronstedtite abundance decreases with increasing alteration.[4]

Cronstedtite- Cornwall, England

References[edit]

  1. ^ a b Webmineral.com
  2. ^ Mindat.org
  3. ^ American Mineralogical Society
  4. ^ Browning et al. (1996) Geochimica et Cosmochimica Acta