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
CategoryArsenate mineral
Formula
(repeating unit)
KCdCu5(AsO4)4(H2AsO4)·2H2O
IMA symbolArb[1]
Strunz classification8.DH.50 08
Dana classification42.09.02.03
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/m
Unit cella = 9.81, b = 10.034
c = 9.975 [Å]; β = 101.83°; Z = 2
Identification
ColorBlue
Crystal habitPlaty
Cleavage{100} good
Mohs scale hardness3
LusterVitreous
StreakPale blue
DiaphaneityTransparent
Specific gravity4
Optical propertiesBiaxial (-)
Refractive indexnα = 1.72, nβ = 1.749, nγ = 1.757
Birefringenceδ = 0.037
References[2][3]

References

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  1. ^ 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.
  2. ^ Andyrobertsite. Mindat.org
  3. ^ a b Andyrobertsite. Webmineral.com