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Cronstedite France.jpg
Cronstedtite - Salsigne Mine - France
Category Silicate minerals
(repeating unit)
Strunz classification 9.ED.15
Crystal system Trigonal
Crystal class Ditrigonal pyramidal (3m)
(same H-M symbol)
Space group P31m
Unit cell a = 5.486 Å,
c = 7.095 Å; Z = 1[1]
Color Black, dark brown-black, green-black
Cleavage Perfect on {001}
Tenacity Elastic
Luster Sub-Metallic
Streak Dark olive green
Diaphaneity Translucent
Specific gravity 3.34 - 3.35
Optical properties Biaxial (-)
Refractive index nα = 1.720 nβ = 1.800 nγ = 1.800
Birefringence δ = 0.080
Pleochroism Visible
Dispersion r < 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


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