Ferrogedrite
Amphibole, double chain inosilicate mineral / From Wikipedia, the free encyclopedia
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Ferrogedrite is an amphibole mineral with the complex chemical formula of ☐Fe2+2(Fe2+3Al2)(Si6Al2)O22(OH)2. It is sodium and calcium poor, making it part of the magnesium-iron-manganese-lithium amphibole subgroup. Defined as less than 1.00 apfu (atoms per formula unit) of Na + Ca[5] and consisting of greater than 1.00 apfu of (Mg, Fe2+, Mn2+, Li) separating it from the calcic-sodic amphiboles.[6]: 12–78 It is related to anthophyllite amphibole and gedrite through coupled substitution of (Al, Fe3+) for (Mg, Fe2+, Mn) and Al for Si.[6] and determined by the content of silicon in the standard cell.[5]
Quick Facts General, Category ...
Ferrogedrite | |
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General | |
Category | Inosilicates Amphibole |
Formula (repeating unit) | ☐Fe2+2(Fe2+3Al2)(Si6Al2)O22(OH)2 |
Strunz classification | 9.DD.05 |
Crystal system | Orthorhombic |
Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
Space group | Pnma |
Unit cell | a = 18.52 Å, b = 17.94 Å, c = 5.31 Å; Z = 4 |
Identification | |
Color | Pale greenish-gray to brown |
Crystal habit | Crystals prismatic to bladed; fibrous |
Cleavage | Perfect on {210}, with 54° and 126° intersections |
Tenacity | Brittle |
Mohs scale hardness | 5.5–6 |
Luster | Vitreous |
Streak | Gray white |
Diaphaneity | Transparent to translucent |
Specific gravity | 3.566 |
Optical properties | Biaxial (-) |
Refractive index | nα = 1.642 - 1.694 nβ = 1.649 - 1.710 nγ = 1.661 - 1.722 |
Birefringence | δ = 0.019 - 0.028 |
Pleochroism | X = pale green; Y = brownish green; Z = greenish blue |
2V angle | Measured: 82° |
Dispersion | r < v |
References | [1][2][3][4] |
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