Cronstedtite
Phyllosilicate mineral in the serpentine subgroup
From Wikipedia, the free encyclopedia
Cronstedtite is a complex iron silicate mineral belonging to the serpentine group of minerals. Its chemical formula is Fe2+
2Fe3+
(Si,Fe3+
O
5)(OH)
4.
CategoryPhyllosilicate minerals
GroupKaolinite-Serpentine group, serpentine subgroup
FormulaFe2+
2Fe3+
(Si,Fe3+
O
5)(OH)
4
2Fe3+
(Si,Fe3+
O
5)(OH)
4
| Cronstedtite | |
|---|---|
Cronstedtite – Salsigne Mine – France | |
| General | |
| Category | Phyllosilicate minerals |
| Group | Kaolinite-Serpentine group, serpentine subgroup |
| Formula | Fe2+ 2Fe3+ (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 | |
| 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 | [2][3][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]
