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.[2]

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
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	[1][2]