Gedrite
| Gedrite | |
|---|---|
| General | |
| Category | Inosilicate |
| Formula (repeating unit) | (Mg;Fe2+)2[(Mg;Fe2+)3Al2](Si6Al2)O22(OH)2 |
| Crystal system | Orthorhombic |
| Space group | Orthorhombic 2/m 2/m 2/m |
| Unit cell | a = 18.59 Å, b = 17.89 Å, c = 5.3 Å; Z = 4 |
| Identification | |
| Color | White, gray, brown, green |
| Crystal habit | Bladed and prismatic crystals; fibrous and sheath like aggregates. |
| Cleavage | 56 and 126° - good; {210} perfect |
| Fracture | Splintery |
| Mohs scale hardness | 5.5 - 6 |
| Luster | Vitreous to silky |
| Diaphaneity | Translucent, will transmit light on thin edges. |
| Specific gravity | 3.18 - 3.33 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.671 nβ = 1.681 nγ = 1.690 |
| Birefringence | δ = 0.019 |
| Pleochroism | Weak to moderate |
| 2V angle | Measured: 75° |
| References | [1][2][3] |
Gedrite is a silicate mineral of the amphibole group with formula: (Mg;Fe2+)2[(Mg;Fe2+)3Al2](Si6Al2)O22(OH)2.
Gedrite occurs in contact and medium to high grade metamorphic rocks in association with garnet, cordierite, anthophyllite, cummingtonite, sapphirine, sillimanite, kyanite, quartz, staurolite and biotite.[1]
Gedrite was first described for an occurrence in Gedres, France in 1836.[2]
References
- ^ a b http://www.handbookofmineralogy.org/pdfs/gedrite.pdf Handbook of Mineralogy
- ^ a b http://webmineral.com/data/Gedrite.shtml Webmineral
- ^ http://www.mindat.org/min-1665.html Mindat
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