Gormanite
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| Gormanite | |
|---|---|
 Gormanite from the Doce valley, Minas Gerais, Brazil (size: 4.2 × 4.2 × 3.0 cm) | |
| General | |
| Category | Phosphate minerals |
| Formula | (Fe,Mg)3Al4(PO4)4(OH)6·2H2O |
| IMA symbol | Gm[1] |
| Strunz classification | 8.DC.45 |
| Crystal system | Triclinic |
| Crystal class | Pedial (1) (same H-M symbol) |
| Space group | P1 |
| Unit cell | a = 11.77, b = 5.11 c = 13.57 [Å]; α = 90.45° β = 99.15°, γ = 90.05°; Z = 2 |
| Identification | |
| Color | Blue green |
| Crystal habit | Aggregates of acicular crystals; pseudomonoclinic |
| Twinning | Polysynthetic around [010] |
| Cleavage | {001} indistinct |
| Fracture | Splintery |
| Tenacity | Brittle |
| Mohs scale hardness | 4–5 |
| Luster | Sub-vitreous, greasy |
| Streak | Pale green |
| Diaphaneity | Semitransparent |
| Specific gravity | 3.10–3.13 |
| Optical properties | Biaxial (−) |
| Refractive index | nα = 1.619 nβ = 1.653 nγ = 1.660 |
| Birefringence | .041 |
| Pleochroism | Strong, X colorless, Y blue, Z colorless |
| 2V angle | Measured: 53° |
| References | [2][3][4] |
Gormanite is a phosphate mineral with the formula (Fe,Mg)3Al4(PO4)4(OH)6·2H2O. It was named after the University of Toronto professor Donald Herbert Gorman (1922–2020).
