Marshite
Marshite (CuI) is a naturally occurring isometric halide mineral with occasional silver (Ag) substitution for copper (Cu). Solid solution between the silver end-member miersite and the copper end-member marshite has been found in these minerals from deposits in Broken Hill, Australia. The mineral's name is derived from the person who first described it, an Australian mineral collector named Charles W. Marsh. Marsh drew attention to native copper iodide (Marshite) in the 1800s emphasizing its natural occurrence, it is not to be confused with copper (I) iodide a substance commonly synthesized in laboratory settings.
| Marshite | |
|---|---|
Exceptionally well crystallized specimen of the rare copper iodide marshite from the Rubtsovskoe Deposit, Altaiskii Krai, Western Siberia, Russian Federation. | |
| General | |
| Category | Halide mineral |
| Formula (repeating unit) | CuI |
| IMA symbol | Msh |
| Strunz classification | 3.AA.05 |
| Dana classification | 9.1.7.3 |
| Crystal system | Isometric |
| Crystal class | Hextetrahedral (43m) |
| Space group | F43m |
| Unit cell | a = 6.05 Å (untwinned a = 6.6063(1) Å); Z=4 |
| Identification | |
| Color | Honey-yellow, exposed to air pink-red to brick-red |
| Crystal habit | Tetrahedral crystals, cubo-octahedral, crusts |
| Twinning | On {111} |
| Cleavage | {011} perfect |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 2.5 |
| Luster | Adamantine, greasy |
| Streak | Yellow |
| Diaphaneity | Transparent |
| Specific gravity | 5.68 |
| Density | 5.68 g/cm3 (measured), 5.71 g/cm3 (calculated) |
| Optical properties | Isotropic |
| Ultraviolet fluorescence | Dark red (SW, LW) |
| References | |
One of marshite's distinguishing features is that prior to exposure to air the mineral is a faint honey-yellow color, once exposed to the air however it becomes a brick-red color. Another characteristic useful in identifying marshite is the dark red color it fluoresces under short-wave (SW) and long-wave (LW) ultraviolet light.