Andyrobertsite
Andyrobertsite is a rare, complex arsenate mineral with a blue color. It is found in the Tsumeb mine in Namibia and named after Andrew C. Roberts (b. 1950), mineralogist with the Geological Survey of Canada. A Ca-rich analogue (with Ca instead of Cd) is called calcioandyrobertsite and has a more greenish tint.[3]
| Andyrobertsite | |
|---|---|
 A mixture of andyrobertsite (blue) and calcioandyrobertsite (green), holotype specimen; size: 3.3×2.2×1.0 mm | |
| General | |
| Category | Arsenate mineral |
| Formula (repeating unit) | KCdCu5(AsO4)4(H2AsO4)·2H2O |
| IMA symbol | Arb[1] |
| Strunz classification | 8.DH.50 08 |
| Dana classification | 42.09.02.03 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | P21/m |
| Unit cell | a = 9.81, b = 10.034 c = 9.975 [Å]; β = 101.83°; Z = 2 |
| Identification | |
| Color | Blue |
| Crystal habit | Platy |
| Cleavage | {100} good |
| Mohs scale hardness | 3 |
| Luster | Vitreous |
| Streak | Pale blue |
| Diaphaneity | Transparent |
| Specific gravity | 4 |
| Optical properties | Biaxial (-) |
| Refractive index | nα = 1.72, nβ = 1.749, nγ = 1.757 |
| Birefringence | δ = 0.037 |
| References | [2][3] |
References
- Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- Andyrobertsite. Mindat.org
- Andyrobertsite. Webmineral.com
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