| Roscoelite | |
|---|---|
_(16562912783).jpg) Roscoelite and gold | |
| General | |
| Category | Phyllosilicateminerals,micagroup |
| Formula | K(V3+,Al,Mg)2AlSi3O10(OH)2 |
| IMA symbol | Rcl[1] |
| Strunz classification | 9.EC.15 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (sameH-M symbol) |
| Space group | C2/m |
| Identification | |
| Formula mass | 426.53 g/mol |
| Colour | olive-green to green-brown |
| Crystal habit | scales, fans,druses,rosettes, fibrous orfelted aggregate. |
| Cleavage | Perfect plane {0,0,1} |
| Fracture | platy |
| Mohs scale hardness | 1 |
| Lustre | pearly |
| Diaphaneity | semi-transparent totranslucent |
| Specific gravity | 2.92 - 2.96 |
| Optical properties | Biaxial (-) |
| Refractive index | nα=1.60 nβ=1.66 nγ=1.67 |
| Birefringence | δ = |
| Pleochroism | olive green to green-brown |
| Fusibility | loses water |
Roscoelite is a green mineral from themica group that containsvanadium.The chemical formula isK(V3+,Al,Mg)2AlSi3O10(OH)2.[2]Crystals of roscoelite take on themonoclinic form, and are from the 2/mpoint group.The appearance is semi transparent to translucent coloured olive brown to green brown. Thelustre is pearly. The mineral showspleochroism with X showing green-brown, and Y and Z axes showing olive-green colour. The mineral was named afterHenry Enfield Roscoe who first produced vanadium metal.
Roscoelite is amuscovite withaluminium substituted with vanadium. Vanadium can also be substituted bymagnesium,iron, ormanganese.
It is soft and the density is 2.93±0.01. Theunit cell has dimensions
with an angle between axes of β=101.0°. The tetrahedral cation-oxygen atom distance is 164.1 pm, The distance from the cation to the oxygen in the octahedral plan is 202 pm.[3]
Two kinds of mineral deposits contain roscoelite, eithergold-silver-tellurium low temperature epithermal deposits where it occurs along withquartz,fluorite,pyrite andcarbonates, or oxidized low temperatureuranium-vanadiumores insedimentary rocks, where it occurs withcorvusite,hewettite,carnotite andtyuyamunite. Roecoelite is considered agangue mineral of no value when found with gold.[4] However it has also been used as a vanadium ore.
In the Mt. Kare mine in New Guinea the mineral occurs with gold and is an important maker of gold deposits. The temperature of the geothermal fluid that deposited the roscoelite was from 127 to 167 °C (261 to 333 °F). The fluid contained a high level ofsalt and also containedcarbon dioxide,methane,carbonyl sulfide and other minor amounts of rock forming elements.[5]
The mineral has been found in numerous places in US, Australia, Japan, Gabon, Fiji, New Guinea[6] and Czech Republic. In theUnited States, it was the principalvanadium ore mineral at the mines atPlacerville, Colorado. In Australia roscoelite has been found atKalgoorlie,Radium Hill and the Kintore Open Cut atBroken Hill.[citation needed]
