Gedrite
[]Mg5Al2(Si6Al2)O22(OH)2 [CNMNC approved formula]
Named for the locality: Heas Valley near Gedres, France. First published in 1836. Redefined per nomenclature of amphiboles (IMA, 1978).
| IMA status : | Redefined IMA Approved; 1978 () |
| CLASSIFICATION | |
| Dana (8th edition) : |
66.01.02.06 |
| (66) Inosilicate Double-Width Unbranched Chains, W=2 | |
| (66.01) with P=2 amphibole configuration | |
| (66.01.02) | |
| Nickel-Strunz (10th edition) : |
09.DE.05 |
| (09) Silicates | |
| (09.D) Inosilicates* Structural terminology per Liebau (1985) | |
| (09.DE) with 2-periodic double chains, Si4O11; Clinoamphiboles | |
| Crystal system: | Orthorhombic System |
| Point group (H-M): | mmm (or 2/m 2/m 2/m) — dipyramidal |
| Space group: | Pnma |
| Unit cell: | a = 18.59Å, b = 17.89Å, c = 5.3Å, Z = 4 |
| Crystal Habit: | As bladed and prismatic crystals; fibrous and semi-sheaf-like aggregates. |
| Color: | White, gray, brown, green; colorless, gray, or brown in thin section |
| Diaphaneity: | Transparent to translucent |
| Luster: | Vitreous |
| Hardness (Mohs): | 5.5 - 6 |
| Measured Density: | 3.15 - 3.259 g/cm3 |
| Cleavage: | Perfect on {210}, intersecting at 54° and 126°, imperfect on {010}, {100} |
| Tenacity: | Brittle |
| Polymorphism and Series: | Forms a series with magnesio-gedrite and ferro-gedrite. |
| Geologic Setting: | Widespread in medium- to high-grade metamorphic rocks; in metasomatized contact metamorphic rocks. |
| Mineral Association: | Garnet, cordierite, "hornblende" anthophyllite, cummingtonite, sapphirine, sillimanite, kyanite, quartz, staurolite, biotite. |
| Other Properties: | Gemstone Unlikely Available. |
Matrix with masses of small brownish gedrite throughout.Origin: Moapa District, Clark Co., Nevada, U.S.A.
Sample size: 3.3 x 2.3 x 1.2 cm
Photo: Dan Weinrich
(zoom-in of above)