Mixite

Mixite is a rare copper bismuth arsenate mineral with formula: BiCu₆(AsO₄)₃(OH)₆·3(H₂O). It crystallizes in the hexagonal crystal system typically occurring as radiating acicular prisms and massive encrustations. The color varies from white to various shades of green and blue. It has a Mohs hardness of 3.5 to 4 and a specific gravity of 3.8. It has an uneven fracture and a brilliant to adamantine luster.

Mixite
Turquoise-blue mixite, Laurium, Greece. Size: 6.8 x 5.0 x 3.6 cm.
General
Category	Arsenate mineral
Formula	BiCu6(AsO4)3(OH)6·3(H2O)
IMA symbol	Mix[1]
Strunz classification	8.DL.15
Crystal system	Hexagonal
Crystal class	Dipyramidal (6/m) (same H-M symbol)
Space group	P63/m
Unit cell	a = 13.646(2) Å, c = 5.920(1) Å; Z = 2
Identification
Color	Blue to emerald-green, pale green, white
Crystal habit	Acicular crystals often in radial clusters
Fracture	Uneven
Mohs scale hardness	3–4
Luster	Vitreous
Streak	Pale green
Diaphaneity	Transparent to translucent
Specific gravity	3.79–3.83
Optical properties	Uniaxial (+)
Refractive index	nω = 1.743 – 1.749 nε = 1.810 – 1.830
Birefringence	δ = 0.067
Pleochroism	O = colorless, E = bright green
References	[2][3][4]

It occurs as a secondary mineral in the oxidized zones of copper deposits. Associated minerals include: bismutite, smaltite, native bismuth, atelestite, erythrite, malachite and barite.^[2]

It was discovered in 1879 near J´achymov, Czech Republic by mine engineer Anton Mixa.^[5] Mixite has also been found in Argentina,^[6] Australia,^[7] Austria,^[8] France,^[9] Germany,^[10] Greece,^[11] Hungary,^[12] Italy,^[13] Japan,^[14] Mexico,^[15] Namibia,^[16] Poland,^[17] Spain,^[18] Switzerland,^[19] the United Kingdom,^[20] and the United States.^[21]

Mixite is the namesake member of the mixite mineral group, which has the general chemical formula Cu²⁺₆A(TO₄)₃(OH)₆·3H₂O, where A is a REE, Al, Ca, Pb, or Bi, and T is P or As. In addition to mixite, this mineral group contains the isostructural minerals agardite-(Y),^[22][23] agardite-(Ce),^[24] agardite-(Nd),^[25] agardite-(La),^[26] calciopetersite,^[27] goudeyite,^[28] petersite-(Ce),^[29] petersite-(Y),^[23][30] plumboagardite,^[31] and zálesíite.^[32]