MINERALS/Arsenates 507 Table Examples of common arsenate groups Group General formula Examples Crystal system(s) Point group(s) Adamite X(AsO4)(OH) X Cu,Zn,Mn,Zn Triclinic Orthorhombic Adelite XYAsO4OH X Ca,Pb Y Cu,Zn X5(AsO4)3(F,Cl,OH) X Ca,(Ba,Ca,Pb),(Ca,Pb),(Ca,Sr),Pb Adamite Olivenite Paradamite Austenite Conichalcite Duftite Clinomimetite Mimetite Hedyphane Arthurite Cobaltarthurite Ojuelaite Heinrichite Kahlerite Uranospinite Zuenerite Beudantite Gallobeudantite Hidalgoite Arsenocrandallite Philipsbornite Hexagonal bar 2/m 2/m 2/m 2/m 2/m 2/m 222 6/m Monoclinic 2/m Monoclinic tetragonal 2/m 2/m 4/m 2/m 2/m bar Apatite pyromorphite Arthurite X Fe2(AsO4)2(O,OH)2 2H2O X Cu,Fe,Mn,Zn Autunite X(UO2)2(AsO4)2 12H2O X H,Mg,Fe,Cu,Ca,Ba,Mn,1=2(HAl) Beudantite XY3(AsO4PO4)SO4(OH)6 X Ca,Ba,Ce,Pb,Sr,H3O Y Fe,Al,Ga XAl3(AsO4)2(OH,F)1–6 15H2O X (Ca,Sr),(Sr,Ca,Ba),Ba,Pb,(Ce,La),Fe Crandallite Meta autunite X(UO2)1–2(AsO4)2 8H2O X Mg,Fe,Co,Cu,Ca,Ba,K,Na,Zn Mixite XCu6(AsO4)3(OH)6 3H2O X Bi,Al,Ca,Ce,La,Y,Nd,Th Pseuomalachite X3–5(AsO4)2(OH)3–4 X Cu,Mn Roselite Ca2X(AsO4)2 2H2O Co,Mn,Mg,Zn X Variscite XAsO4 2H2O X Al,Fe,In Vivianite X3(AsO4)2 8H2O X Co,Fe,Mg,Ni,Zn mineral streak is often green or a shade of green (bluish, olive, pale), but grey, pale blue, brown red and yellow, orange yellow, and white are known Arsenate crystals tend to range from transparent to translucent, and some opaque varieties have also been documented Luster is adamantine, dull (in massive or powdery varieties), greasy, pearly, resinous, silky, sub-adamantine, or vitreous Hardness is generally low, ranging from 1.5 up to 4.5, and specific gravity tends to be slightly below average to heavy for translucent minerals (2.4 to 6.7) A huge variety of crystal habits have been described for the arsenates Examples include acicular, botryoidal, fibrous, foliated, micaceous, prismatic, radiating, striated blade and tabular single crystals, Abernathyite Metalodevite Metanovacekite Agardite Goudeyite Mixite Cornwallite Arsenoclasite Brandtite Roselite Zincroselite Mansfieldite Scorodite Yanomamite Annabergite Erythrite Kottingite Hornesite Parasymplesite Orthorhombic Trigonal Trigonal Tetragonal 3m 3m 3m 2/m 4/m 2/m 2/m Hexagonal Triclinic, monoclinic Monoclinic 2/m 222 2/m Orthorhombic 2/m 2/m 2/m Monoclinic 2/m aggregates, clusters, or masses (Figure 1) Crystal faces exhibit diverse termination surfaces: domes with bipyramids, triangles, double triangles, pinacoids, and wedges with complex facets Several varieties are twinned Most commonly, however, the minerals occur as crusts, globular aggregates, nodules, or powdery masses with little crystal shape Cleavage ranges from absent to poor or perfect in one or two directions Fracture is described as conchoidal, fibrous, flaky, or lamellar The arsenate adamite (Zn2AsO4(OH)) is well known for its fluorescent properties Arsenates belonging to the autinite group (e.g., meta-zeunerite, walpurgite, zeunerite) are radioactive due to the uranium in their structures