Marshite | |
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![]() 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[1] |
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 | [2][3][4][5] |
Marshite (CuI) is a naturally occurring isometric halide mineral with occasional silver (Ag) substitution for copper (Cu).[6][7] 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.[8] The mineral's name is derived from the person who first described it, an Australian mineral collector named Charles W. Marsh.[2][3][4] 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.[9][10]
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.[2][3] Another characteristic useful in identifying marshite is the dark red color it fluoresces under short-wave (SW) and long-wave (LW) ultraviolet light.[2][4]