Bobdownsite
| Bobdownsite | |
|---|---|
| General | |
| Category | Phosphate minerals |
|
Formula (repeating unit) |
Ca9(Mg)(PO4)6(PO3F) |
| Strunz classification | 8.AC.45 |
| Dana classification | 38.3.4.8 |
| Crystal system | Trigonal |
| Crystal class | Ditrigonal pyramidal (3m) (same H-M symbol) |
| Space group | R3c |
| Unit cell | a = 10.3224 Å, c = 37.070 Å; Z = 6 |
| Identification | |
| Formula mass | 1,054.36 g/mol |
| Color | Colorless, gray-white, light pink, light yellow |
| Crystal habit | tabular, euhedral crystals |
| Cleavage | None |
| Fracture | uneven and subconchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 5 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent |
| Specific gravity | 3.14 to 3.16 |
| Optical properties | uniaxial (-) |
| Refractive index | nω = 1.625(2) nε = 1.622(2) |
| Ultraviolet fluorescence | none |
| Diagnostic features | unit cell dimension |
| References | |
Bobdownsite is the fluorine bearing mineral of the whitlockite group of phosphate minerals whose formula is Ca9(Mg)(PO4)6(PO3F). It is isotypic with whitlockite and was misidentified as such until proper chemical analysis. Whitlockites structure and relationships with other phosphate compounds has been extensively studied. Bobdownsite was first recovered from Big Fish River, Yukon, Canada from a Lower Cretaceous outcrop of bedded ironstones and shales. Bobdownsite is named after Robert Terrace Downs a professor of mineralogy in the Department of Geosciences at the University of Arizona, who lived and worked in the Yukon Territory in the 1970s. Bobdownsite is unique because it is the first known naturally forming phosphate to contain a P-F bond.
Bobdownsite is closely related to whitlockite and merrillite.
Member of the whitlockite group:
Other members of group:
Bobdownsite is originally found from Big Fish River, Yukon, Canada (about Latitude 68°28'N, Longitude 136°30'W). Bobdownsite occurs in a vein from an east- west- trending faulted vein. Samples recovered from this exposure are found with Lower Cretaceous bedded ironstones and shales. Bobdownsite is a phosphate mineral with its exposure downstream from phosphate nodule slopes. The vein at the exposure is composed of anhedral and euhedral crystals and is 0 to 4 cm wide. It occurs associated with siderite, lazulite, kulanite, gormanite, quartz and collinsite. Bobdownsite has also been reported from the Tip Top mine of Custer County, South Dakota. Furthermore, it has been found with other witlockite group minerals in Martian meteorites.
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