| Subclass: ArsenatesArsenate mineral, any of a group of naturally occurring compounds of arsenic, oxygen, and various metals, most of which are rare, having crystallized under very restricted conditions. At the mineralogically famous Långban iron and manganese mines in central Sweden, more than 50 species of arsenate minerals have been described, many peculiar to the locality. Such compounds occur in open cavities and resulted from the reaction of arsenic acid (H3AsO4) upon pyrochroite [manganese hydroxide; Mn(OH)2] at moderate to low temperature. Arsenates at other localities are often oxidation products of arsenide ores and are deposited at low temperatures in late-stage veins and open cavities.
Only a few arsenate minerals have economic importance. Because the transition metals (e.g., cobalt, copper, nickel) give brilliant colour to some of the arsenates, these can be used to advantage in prospecting; such arsenate oxidation products, or blooms, as erythrite (bright pink) and annabergite (green) are indicators of nickel and cobalt arsenide ores. Many of the nickel and cobalt deposits at Sudbury and Cobalt, Ont., were located in this manner.
The arsenate minerals, which are salts of arsenic acid, contain arsenate groups (AsO4) in which four oxygen (O) atoms are arranged at the corners of a tetrahedron about a central arsenic (As) atom. Each arsenate tetrahedron has a net electric charge of -3, which is neutralized by large, positively charged metal ions (e.g., calcium, manganese, or ferrous iron) outside the tetrahedron. Unlike the similar silicate tetrahedra, which link to form chains, sheets, rings, or frameworks, arsenate tetrahedra are insular.
The crystal structure of the arsenate minerals is very similar to that of the phosphate and vanadate minerals; indeed, many arsenate minerals form solid solutions with both the phosphates and the vanadates.
| Name
| Colour
| Lustre
| Image
| Crystal system
| | Adamite
Zn2(AsO4)(OH)
| Ideally white, colourless, frequently pale yellow
| Vitreous, Sub-Vitreous, Waxy, Greasy
| 
| Orthorhombic
| | Adelite
CaMg(AsO4)(OH)
| Colourless white, grey, bluish grey, yellowish grey
| Vitreous, Greasy
| 
| Orthorhombic
| | Agardite
CeCu6(AsO4)3(OH)6 · 3H2O
| light green, yellowish green
| Sub-Vitreous, Resinous, Silky
| 
| Hexagonal
| | Annabergite
Ni3(AsO4)2 · 8H2O
| Green, light grey to light apple green, white; pale rose red when rich in cobalt
| Sub-Adamantine, Sub-Vitreous, Pearly, Earthy
| 
| Monoclinic
| | Arsenosiderite
FeAs2
| Steel gray to silver white
| Metallic
| 
| Orthorhombic
| | Arsenoclasite
Mn52+(AsO4)2(OH)4
| Red
| Vitreous
| 
| Orthorhombic
| | Arsenocrandallite
CaAl3(AsO4)(AsO3OH)(OH)6
| White, creamy yellowish-white, also blue to bluish-green
| Sub-Vitreous, Resinous, Waxy, Dull
| 
| Trigonal
| | Arsenoflorencite
CeAl3(AsO4)2(OH)6
| Colourless to white, light brown
| Sub-Vitreous, Resinous, Waxy, Dull
| 
| Trigonal
| | Arsentsumebite
Pb2Cu(AsO4)(SO4)(OH)
| Emerald-green, grass-green, apple-green, pale bluish green
| Vitreous
| 
| Monoclinic
| | Arthurite
CuFe23+(AsO4)2(OH)2 · 4H2O
| Apple-green, emerald-green, pale olive-green
| Vitreous
| 
| Monoclinic
| | Atelestite
Bi2(AsO4)O(OH)
| Sulphur-yellow to yellowish-green, yellow-brown
| Adamantine, Resinous
| 
| Monoclinic
| | Austinite
CaZn(AsO4)(OH)
| Colorless to pale yellowish white or bright green; colourless in transmitted light.
| Sub-Adamantine, Sub-Vitreous, Greasy, Silky
| 
| Orthorhombic
| | Bayldonite
PbCu3(AsO4)2(OH)2
| Green, apple-green, yellow-green; dark green to black (crystals)
| Resinous, Waxy, Greasy
| 
| Monoclinic
| | Berzeliite
(NaCa2)Mg2(AsO4)3
| Yellow, Orange, colorless, brownish-orange
| Sub-Vitreous, ResinousGreasy
| 
| Isometric
| | Carminite
PbFe23+(AsO4)2(OH)2
| Carmine-red, terra cotta-red, reddish brown; red in transmitted light
| Vitreous, Pearly
| 
| Orthorhombic
| | Cafarsite
Ca5.9Mn1.7Fe3Ti3(AsO3)12 · 4-5H2O
| Dark brown
| Vitreous
| 
| Isometric
| | Caryinite
(Na,Pb)(Ca,Na)CaMn22+(AsO4)3
| Brown to yellowish brown; light yellow-brown in transmitted light
| ResinousGreasy
| 
| Monoclinic
| | Duftite
PbCu(AsO4)(OH)
| Olive-green, grey-green; light apple-green in transmitted light.
| Sub-Vitreous, ResinousWaxy, Dull
| 
| Orthorhombic
| | Eveite
Mn22+(AsO4)(OH)
| apple green, pale yellow
| ResinousGreasy
| 
| Orthorhombic
| | Holdenite
(Mn2+,Mg)6Zn3(AsO4)2(SiO4)(OH)8
| Pink, yellowish red, deep red; pink in transmitted light
| Sub-Vitreous, ResinousWaxy
| 
| Orthorhombic
| | Kottigite
Zn3(AsO4)2 · 8H2O
| Should be colorless, but frequently is Carmine-red, red-orange, brown
| ResinouWaxy, Silky
| 
| Monoclinic
| | Legrandite
Zn2(AsO4)(OH) · H2O
| Yellow to colourless; pale yellow to colourless in transmitted light
| Vitreous, Sub-Vitreous, Resinous Waxy
| 
| Monoclinic
| | Leiteite
Zn(As2O4)
| white to colorless
| Sub-Vitreous, Resinous, Waxy, Dull
| 
| Monoclinic
| | Mixite
BiCu6(AsO4)3(OH)6 · 3H2O
| pale green, blue-green, emerald-green, white; light green to colourless in transmitted light
| Vitreous
| 
| Hexagonal
| | Nealite
Pb4Fe2+(As3+O3)2Cl4 · 2H2O
| Yellow brown to orange brown
| Adamantine, Vitreous, Sub-Vitreous
| 
| Triclinic
| | Olivenite
Cu2(AsO4)(OH)
| Olive green to yellow or brown, gray-green, grayish white; light green in transmitted light
| Sub-Adamantine, Sub-Vitreous, Resinous, Silky, Pearly
| 
| Monoclinic
| | Tyrolite
Ca2Cu9(AsO4)4(CO3)(OH)8 · 11H2O
| Turquoise-blue, blue-green; light bluish green in transmitted light
| Vitreous, Silky, Pearly
| 
| Monoclinic
| | Wendwilsonite
Ca2Mg(AsO4)2 · 2H2O
| Pale pink to red
| Vitreous
| 
| Monoclinic
| | Zincroselite
| Colourless, white
| Vitreous
| 
| Monoclinic
|
Date: 2015-12-24; view: 2358
|
