Gordaite
| Gordaite | |
|---|---|
| General | |
| Category | Sulfate mineral |
|
Formula (repeating unit) |
NaZn4(SO4)(OH)6Cl·6H2O |
| 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 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 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.
The 1998 Nasdala article examines the ALV 1457-5R sample found on the sea floor of the Juan de Fuca Ridge. The sample itself was taken from a sulfide chimney with mass of about 2.5 kg. The chimney was composed of about 98% permeable sulfides and 2% sulfates. The sulfides were primarily composed of iron sulfides such as pyrite and sphalerite and were present in the core of the chimney. The sulfate portions were found in concentric layers on the outside of the sample, alternating between [Zn4(OH)6(SO4)Cl]- and [Na(H2O)6]- interlayers.
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