Cronstedtite

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Cronstedtite
Cronstedite France.jpg
Cronstedtite - Salsigne Mine - France
General
Category Silicate minerals
Formula
(repeating unit)
Fe2+2Fe3+(Si,Fe3+O5)(OH)4
Strunz classification 09.ED.15
Crystal symmetry Trigonal 3m ditrigonal pyramidal
Unit cell a = 5.486 Å, c = 7.095 Å; Z = 1[1]
Identification
Color Black, dark brown-black, green-black
Crystal system Trigonal
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

References[edit]

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