Cronstedtite

Last updated
Cronstedtite
Cronstedite France.jpg
Cronstedtite – Salsigne Mine – France
General
Category Phyllosilicate minerals, kaolinite-serpentine group, serpentine subgroup
Formula Fe2+
2
Fe3+
(Si,Fe3+
O
5
)(OH)
4
IMA symbol Cro [1]
Strunz classification 9.ED.15
Crystal system Trigonal
Crystal class Ditrigonal pyramidal (3 m)
(same H-M symbol)
Space group P31m (no. 157)
Unit cell a = 5.486 Å,
c = 7.095 Å; Z = 1 [2]
Identification
ColorBlack, 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 propertiesBiaxial (−)
Refractive index nα = 1.720 nβ = 1.800 nγ = 1.800
Birefringence δ = 0.080
Pleochroism Visible
Dispersion r < v moderate
References [2] [3] [4]

Cronstedtite is a complex iron silicate mineral belonging to the serpentine group of minerals. Its chemical formula is Fe2+
2
Fe3+
(Si,Fe3+
O
5
)(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. [5]

Cronstedtite - Cornwall, England Cronstedtite Pisani.jpg
Cronstedtite – Cornwall, England

See also

References

  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols" . Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
  2. 1 2 Webmineral.com
  3. Mindat.org
  4. American Mineralogical Society
  5. Browning, Lauren B.; McSween, Harry Y.; Zolensky, Michael E. (1996). "Correlated alteration effects in CM carbonaceous chondrites". Geochimica et Cosmochimica Acta. 60 (14): 2621–2633. doi:10.1016/0016-7037(96)00121-4. ISSN   0016-7037.