Gordaite
Gordaite is a sulfate mineral composed primarily of hydrous zinc sodium sulfate chloride hydroxide with formula: NaZn4(SO4)(OH)6Cl·6H2O. It was named for the discovery location in the Sierra Gorda district of Chile. Gordaite forms as tabular trigonal crystals.
| Gordaite | |
|---|---|
Pale blue gordaite associated with deep green crystals of herbertsmithite from the San Francisco Mine, Caracoles, Antofagasta Region, Chile. | |
| General | |
| Category | Sulfate mineral |
| Formula (repeating unit) | NaZn4(SO4)(OH)6Cl·6H2O |
| IMA symbol | Gda |
| Strunz classification | 7.DF.50 |
| Crystal system | Trigonal |
| Crystal class | Rhombohedral (3) (same H-M symbol) |
| Space group | P3 |
| Unit cell | a = 8.413, c = 13.095 [Å]; Z = 2 |
| Identification | |
| Color | Colorless to white, pale green with copper substitution |
| Crystal habit | Thin tabular flakes or blades, in rosette aggregates |
| Cleavage | Perfect on {0001} |
| Tenacity | Flexible |
| Mohs scale hardness | 2.5 |
| Luster | Vitreous to pearly |
| Specific gravity | 2.627 |
| Optical properties | Uniaxial (-) |
| Refractive index | nω = 1.561 nε = 1.538 |
| Birefringence | δ = 0.023 |
| References | |
Gordaite first appeared after a research dive in September 1984 from the Juan de Fuca Ridge of the northeastern side of the Pacific Ocean. Gordaite was also described from weathered slag deposits as a result of copper smelting in Hettstedt, Germany. The mineral exhibits a hexagonal shape with clear or white (green if cuprian – Cu2+) crystals ranging from planar to broad habit and has a point group of 3. Gordaite commonly occurs near minerals such as sphalerite, boleite and gypsum. The most recent finding occurred in the San Francisco mine in Chile where copper-zinc sulfide deposits were found.