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The general structural formula for the walentaite group is [((A1yA1’1–y), A2)(H2O)n][Bx(As2)2–x(As3)M1(M2)2(TO4)2(O,OH)7], based on heteropolyhedral layers of configuration [M1(M2)2(TO4)2(O,OH)6], with surface-coordinated species at the B, As2 and As3 sites, and with interlayer hydrated cation groups centred at the A sites. The group is divided into walentaite and halilsarpite subgroups based on T = P5+ and As5+, respectively. Alcantarillaite, (IMA2019-072), [Fe3+0.5□0.5(H2O)4][CaAs3+2(Fe3+2.5W6+0.5)(AsO4)2O7], is a new member of the walentaite group from the Alcantarilla wolframite mine, Belalcázar, Córdoba, Andalusia, Spain. It occurs most commonly as lemon-yellow fillings together with massive scorodite in fissures and cracks in quartz adjacent to löllingite. It is also found as tiny yellow rosettes lining vugs and as spheroids of ultrathin blades. It is associated with scorodite, pharmacosiderite, ferberite and schneiderhöhnite. Optically it is biaxial (–), with α = 1.703(calc), β = 1.800(5), γ = 1.850(5) and 2V = 68(1)° (white light). Dispersion is r > v, moderate. The optical orientation is X = a, Y = c and Z = b. The calculated density is 3.06 g cm–3. Electron microprobe analyses together with crystal structure refinement results gives the empirical formula [Fe3+0.52□0.48(H2O)4][(Ca0.44K0.11Na0.05Fe2+0.24□0.42)As3+1.83][Fe3+2.54Al0.03W6+0.43)((As0.65P0.35)O4)2O5.86(OH)1.14]. Alcantarillaite is orthorhombic, with an average structure described in Imma, and with a = 24.038(8) Å, b = 7.444(3) Å, c = 10.387(3) Å, V = 1858.6(11) Å3 and Z = 4. The structure (wRobs = 0.078 for 651 reflections to a resolution of 0.91 Å) differs most significantly from other walentaite-group members in having an interlayer A2 site occupied. Square-pyramidal polyhedra centred at the A2 sites form edge-shared dimers, (Fe3+)2O4(H2O)4. The dimers share vertices with TO4 anions in the layers on either side to form 8-sided channels along [010] occupied by H2O molecules.

Thermodynamic data for the arsenates of various metals are necessary to calculate their solubilities and to evaluate their potential as arsenic storage media. If some of the less common arsenate minerals have been shown to be less soluble than the currently used options for arsenic disposal (especially scorodite and arsenical iron oxides), they should be further investigated as promising storage media. Furthermore, the health risk associated with arsenic minerals is a function of their solubility and bioavailability, not merely their presence. For all these purposes, solubilities of such minerals need to be known. In this work, a complete set of thermodynamic data has been determined for mansfieldite, AlAsO4·2H2O; angelellite, Fe4(AsO4)2O3; and kamarizaite, Fe3(AsO4)2(OH)3·3H2O, using a combination of high-temperature oxide-melt calorimetry, relaxation calorimetry, solubility measurements, and estimates where possible and appropriate. Several choices for the reference compounds for As for the high-temperature oxide-melt calorimetry were assessed. Scorodite was selected as the best one. The calculated Gibbs free energy of formation (all data in kJ·mol–1) is –1733.4 ± 3.5 for mansfieldite, –2319.2 ± 7.9 for angelellite and –3056.8 ± 8.5 for kamarizaite. The solubility products for the dissolution reactions are –21.4 ± 0.5 for mansfieldite, –43.4 ± 1.5 for angelellite and –50.8 ± 1.6 for kamarizaite. Available, but limited, chemical data for the natural scorodite–mansfieldite solid-solution series hint at a miscibility gap; hence the non-ideal nature of the series. However, no mixing parameters were derived because more data are needed. The solubility of mansfieldite is several orders of magnitude higher than that of scorodite. The solubility of kamarizaite, on the other hand, is comparable to that of scorodite, and kamarizaite even has a small stability field in a pH-pε diagram. It is predicted to form under mildly acidic conditions in acid drainage systems that are not subject to rapid neutralization and sudden strong supersaturation. The solubility of angelellite is high, and the mineral is obviously restricted to unusual environments, such as fumaroles. Its crystallization may be enhancedviaits epitaxial relationship with the much more common hematite. The use of the scorodite–mansfieldite solid solution for arsenic disposal, whether the solid solution is ideal or not, is not practical. The difference in solubility products of the two end-members (scorodite and mansfieldite) is so large that almost any system will drive the precipitation of essentially pure scorodite, leaving the aluminium in the aqueous phase.

The new mineral currierite (IMA2016-030), Na4Ca3MgAl4(AsO3OH)12·9H2O, was found at the Torrecillas mine, Iquique Province, Chile, where it occurs as a secondary alteration phase in association with anhydrite, canutite, chudobaite, halite, lavendulan, magnesiokoritnigite, quartz, scorodite and torrecillasite. Currierite occurs as hexagonal prisms, needles and hair-like fibres up to ∼200 μm long, in sprays. The crystal forms are ﹛100﹜ and ﹛001﹜. Crystals are transparent, with vitreous to silky lustre and white streak. The Mohs hardness is ∼2, tenacity is brittle, but elastic in very thin fibres, and the fracture is irregular. Crystals exhibit at least one good cleavage parallel [001]. The measured density is 3.08(2) g cm -3 and the calculated density is 3.005 g cm -3. Optically, currierite is uniaxial (–) with ω= 1.614(1) and ε= 1.613(1) (measured in white light). The mineral is slowly soluble in dilute HCl at room temperature. The empirical formula, determined from electron-microprobe analyses, is (Na3.95A12.96Ca2.74Mg1.28Fe0.633+Cu0.13K0.08Co0.03Σ11.80 (AS11.685+Sb0.325+Σ12(O56.96Cl0.04)Σ57H30.81. Currierite is hexagonal, P622, with a = 12.2057(9), c = 9.2052(7) Å, V= 1187.7(2) Å3 and Z = 1. The eight strongest powder X-ray diffraction lines are [dobs Å(I)(hkl)]: 10.63(100)(100), 6.12(20)(110), 5.30(15)(200), 4.61(24)(002), 4.002(35)(210), 3.474(29)(202), 3.021(96)(212) and 1.5227(29)(440,334,612). The structure of currierite (R1 = 2.27% for 658 Fo > 4σF reflections) is based upon a heteropolyhedral chain along c in which AlO6 octahedra are triple-linked by sharing corners with AsO3OH tetrahedra. Chains are linked to one another by bonds to 8(4 + 4)-coordinated Na and 8-coordinated Ca forming a three-dimensional framework with large cavities that contain rotationally disordered Mg(H2O)6 octahedra. The chain in the structure of currierite is identical to that in kaatialaite and a geometrical isomer of that in ferrinatrite. The mineral is named in honour of Mr. Rock Henry Currier (1940–2015), American mineral dealer, collector, author and lecturer.

An unworked quartz vein-hosted gold deposit occurs in the Clew bay area of County Mayo, western Ireland. The veins are late-Caledonian in age and transect greenschist-facies poly-deformed Silurian quartzites. The veins contain disseminated arsenopyrite that may be a primary mineral source for elevated levels of arsenic (As) found in groundwater samples recovered from wells related spatially to the gold deposit. Levels from 5 to 188 μg/L (significantly above the 7.5 μg/L threshold for safe drinking water) have been detected. A series of element distribution maps using a scanning electron microscope (Hitachi model S-4700) linked to an energy-dispersive spectrometer (INCA® Oxford Instruments) and mineral distribution maps generated by QEMSCAN® (Quantitative Evaluation of Minerals by Scanning electron microscopy) were used to map the distribution of the primary arsenopyrite and related secondary As-bearing phases. Laser Raman microspectroscopy was used to identify the secondary As-bearing phases. 'Island weathering' of primary arsenopyrite together with hydrated pseudomorphs of arseniosiderite, pharmacosiderite and scorodite after arsenopyrite are recorded. Circulating groundwater hydrates the primary arsenopyrite, providing the release mechanism that forms the secondary As-bearing phases that occur as microfracture infills together with muscovite and biotite. The textural relationships between the primary and secondary As minerals indicate their potential as mineral sources of As that could enter transport pathways leading to its release into groundwater.

Tapiaite (IMA2014-024), Ca5Al2(AsO4)4(OH)4·12H2O, is a new mineral from the Jote mine, Tierra Amarilla, Copiapó Province, Atacama, Chile. The mineral is a late-stage, low-temperature, secondary mineral occurring with conichalcite, joteite, mansfieldite, pharmacoalumite, pharmacosiderite and scorodite in narrow seams and vughs in the oxidized upper portion of a hydrothermal sulfide vein hosted by volcanoclastic rocks. Crystals occur as colourless blades, flattened on {101} and elongated and striated along [010], up to ∼0.5 mm long, and exhibiting the forms {101}, {101} and {111}. The blades are commonly intergrown in subparallel bundles and less commonly in sprays. The mineral is transparent and has a white streak and vitreous lustre. The Mohs hardness is estimated to be between 2 and 3, the tenacity is brittle, and the fracture is splintery. It has two perfect cleavages on {101} and {101}. The calculated density based on the empirical formula is 2.681 g cm–3. It is optically biaxial (+) with α = 1.579(1), β = 1.588(1), γ = 1.610(1) (white light), 2Vmeas = 66(2)° and 2Vcalc = 66°. The mineral exhibits no dispersion. The optical orientation is X ≈ [101]; Y = b, Z ≈ [101]. The electron-microprobe analyses (average of five) provided: Na2O 0.09, CaO 24.96, CuO 0.73, Al2O3 10.08, Fe2O3 0.19, As2O5 40.98, Sb2O5 0.09, H2 O 23.46 (structure), total 100.58 wt.%. In terms of the structure, the empirical formula (based on 32 O a.p.f.u.) is (Ca4.83Cu0.102+Na0.03)Σ4.96(Al2.14Fe0.033+)Σ2.17[(As3.875+Sb0.015+)Σ3.88O16][(OH)3.76(H2O)0.24]Σ4(H2O)10·2H2O. The mineral is easily soluble in RT dilute HCl. Tapiaite is monoclinic, P21/n, with unit-cell parameters a = 16.016(1), b = 5.7781(3), c = 16.341(1) Å, β = 116.704(8)°, V = 1350.9(2) Å3 and Z = 2. The eight strongest lines in the powder X-ray diffraction pattern are [dobs Å(I)(hkl)]: 13.91(100)(101), 7.23(17)(200,002), 5.39(22)(110,011), 4.64(33)(112,211,303), 3.952(42)(113,311,213), 3.290(35)(214,412,114,411), 2.823(39)(303,315) and 2.753(15)(513,115,121,511). The structure of tapiaite (R1 = 5.37% for 1733 Fo > 4σF) contains Al(AsO4)(OH)2 chains of octahedra and tetrahedra that are topologically identical to the chain in the structure of linarite. CaO8 polyhedra condense to the chains, forming columns, which are decorated with additional peripheral AsO4 tetrahedra. The CaO8 polyhedra in adjacent columns link to one another by corner-sharing to form thick layers parallel to {101} and the peripheral AsO4 tetrahedra link to CaO6 octahedra in the interlayer region, resulting in a framework structure.

The new mineral canutite (IMA2013-070), NaMn3[AsO4][AsO3(OH)]2, was found at two different locations at the Torrecillas mine, Salar Grande, Iquique Province, Chile, where it occurs as a secondary alteration phase in association with anhydrite, halite, lavendulan, magnesiokoritnigite, pyrite, quartz and scorodite. Canutite is reddish brown in colour. It forms as prisms elongated on [20] and exhibiting the forms {010}, {100}, {10}, {201} and {102}, or as tablets flattened on {102} and exhibiting the forms {102} and {110}. Crystals are transparent with a vitreous lustre. The mineral has a pale tan streak, Mohs hardness of 2½, brittle tenacity, splintery fracture and two perfect cleavages, on {010} and {101}. The calculated density is 4.112 g cm−3. Optically, canutite is biaxial (+) with α = 1.712(3), β = 1.725(3) and γ = 1.756(3) (measured in white light). The measured 2V is 65.6(4)°, the dispersion is r < v (slight), the optical orientation is Z = b; X ^ a = 18° in obtuse β and pleochroism is imperceptible. The mineral is slowly soluble in cold, dilute HCl. The empirical formula (for tabular crystals from near the mineshaft), determined from electron - microprobe analyses, is (Na1.05Mn2.64Mg0.34Cu0.14Co0.03)∑4.20As3O12H1.62. Canutite is monoclinic, C2/c, a = 12.3282(4), b = 12.6039(5), c = 6.8814(5) Å, β = 113.480(8)°, V = 980.72(10) Å3 and Z = 4. The eight strongest X-ray powder diffraction lines are [dobs Å(I)(hkl)]: 6.33(34)(020), 4.12(26)(21), 3.608(29)(310,31), 3.296(57)(12), 3.150(28)(002,131), 2.819(42)(400,041,330), 2.740(100)(240,02,112) and 1.5364(31)(multiple). The structure, refined to R1 = 2.33% for 1089 Fo > 4σF reflections, shows canutite to be isostructural with protonated members of the alluaudite group.

The new mineral magnesiokoritnigite (IMA 2013-049), ideally Mg(AsO3OH)·H2O, was found at the Torrecillas mine, Salar Grande, Iquique Province, Chile, where it occurs as a secondary alteration phase in association with anhydrite, chudobaite, halite, lavendulan, quartz and scorodite. Crystals of magnesiokoritnigite are colourless to pale-pink, thin to thick laths up to 2 mm long. Laths are elongated on [001], flattened on {010} and exhibit the forms {010}, {110}, {10}, {101}, {031} and {01}. The crystals also occur in dense deep-pink intergrowths. Crystals are transparent with a vitreous lustre. The mineral has a white streak, Mohs hardness of ∼3, brittle tenacity, conchoidal fracture and one perfect cleavage on {101}. The measured and calculated densities are 2.95(3) and 2.935 g cm– 3, respectively. Optically, magnesiokoritnigite is biaxial (+) with α = 1.579(1), β = 1.586(1) and γ = 1.620(1) (measured in white light). The measured 2V is 50(2)° and the calculated 2V is 50°. Dispersion is r < v, medium. The optical orientation is Y ≈ b; Z ^ c = 36° in obtuse β (note pseudomonoclinic symmetry). The mineral is non-pleochroic. The empirical formula, determined from electron-microprobe analyses, is (Mg0.94Cu0.03Mn0.02Ca0.01)Σ 1.00As0.96O5H3.19. Magnesiokoritnigite is triclinic, P, with a = 7.8702(7), b = 15.8081(6), c = 6.6389(14) Å, α = 90.814(6), β = 96.193(6), γ = 90.094(7)°, V = 821.06(19) Å3 and Z = 8. The eight strongest X-ray powder diffraction lines are [dobs Å (I)(hkl)]: 7.96(100)(020), 4.80(54)(101), 3.791(85)(10,210,1,31), 3.242(56)(02,1,012), 3.157(92)(21,30,230), 3.021(61)(11,141,21,221), 2.798(41)(02,032) and 1.908(43)(multiple). The structure, refined to R1 = 5.74% for 2360 Fo > 4σF reflections, shows magnesiokoritnigite to be isostructural with koritnigite and cobaltkoritnigite.

Joteite (IMA2012-091), Ca2CuAl[AsO4][AsO3(OH)]2(OH)2·5H2O, is a new mineral from the Jote mine, Tierra Amarilla, Copiapó Province, Atacama, Chile. The mineral is a late-stage, low-temperature, secondary mineral occurring with conichalcite, mansfieldite, pharmacoalumite, pharmacosiderite and scorodite in narrow seams and vughs in the oxidized upper portion of a hydrothermal sulfide vein hosted by volcanoclastic rocks. Crystals occur as sky-blue to greenish-blue thin blades, flattened and twinned on {001}, up to ~300 μm in length, and exhibiting the forms {001}, {010}, {10}, {20} and {111}. The blades are commonly intergrown in wheat-sheaf-like bundles, less commonly in sprays, and sometimes aggregated as dense crusts and cavity linings. The mineral is transparent and has a very pale blue streak and vitreous lustre. The Mohs hardness is estimated at 2 to 3, the tenacity is brittle, and the fracture is curved. It has one perfect cleavage on {001}. The calculated density based on the empirical formula is 3.056 g/cm3. It is optically biaxial (–) with α = 1.634(1), β = 1.644(1), γ = 1.651(1) (white light), 2Vmeas= 78(2)° and 2Vcalc= 79.4°. The mineral exhibits weak dispersion,r < v. The optical orientation isX≈c*;Y≈b*. The pleochroism isZ(greenish blue) >Y(pale greenish blue) >X(colourless). The normalized electron-microprobe analyses (average of 5) provided: CaO 15.70, CuO 11.22, Al2O38.32, As2O546.62, H2O 18.14 (structure), total 100 wt.%. The empirical formula (based on 19 O a.p.f.u.) is: Ca1.98Cu1.00Al1.15As2.87H14.24O19. The mineral is slowly soluble in cold, concentrated HCl. Joteite is triclinic,P, with the cell parameters:a= 6.0530(2),b= 10.2329(3),c= 12.9112(4) Å,α= 87.572(2),β= 78.480(2), γ = 78.697(2)°,V= 768.40(4) Å3andZ= 2. The eight strongest lines in the X-ray powder diffraction pattern are [dobsÅ(I)(hkl)]: 12.76(100)(001), 5.009(23)(020), 4.206(26)(120,003,121), 3.92(24)(022,02,02), 3.40(25)(13), 3.233(19)(031,023,123,03), 2.97(132,201) and 2.91(15)(22,13). In the structure of joteite (R1= 7.72% for 6003Fo> 4σF), AsO4and AsO3(OH) tetrahedra, AlO6octahedra and Cu2+O5square pyramids share corners to form sheets parallel to {001}. In addition, 7- and 8-coordinate Ca polyhedra link to the periphery of the sheets yielding thick slabs. Between the slabs are unconnected AsO3(OH) tetrahedra, which link the slabs only via hydrogen bonding. The Raman spectrum shows features consistent with OH and/or H2O in multiple structural environments. The region between the slabs may host excess Al in place of some As.

Arsenic is a very common by-product of the processing of Cu, Au and polymetallic ores worldwide, where the ore is roasted (calcined) to remove volatile elements. In southwest England, a diverse range of As-mineral species occur as efflorescent secondary mineral growths on historic calciner buildings. Gypsum occurs as abundant dendritic growths comprising either interlocking blades or tabular crystals. Ca-arsenate minerals are locally very abundant as white colloform masses. Positively identified Ca arsenates include pharmacolite, weilite and haidingerite. Other secondary minerals include arsenolite, scorodite, bukovskyite and an As-bearing potassium alum, together with a wide variety of unidentified minerals, including an Al-As-S phase and As-rich F-bearing phases. Gypsum contains As concentrations up to ~7 wt.%. Efflorescent growth at sites exposed to the prevailing weather systems is less abundant than at sheltered sites. This is interpreted as being due to ‘pressure washing’ of exposed sites by driving rain. Successive concentric growths of gypsum and Ca arsenate on masonry are interpreted as being the result of seasonal crystallization.Understanding both current and historicalmining and mineralprocessing methods is criticalin the evaluation of the potential impact on the modern environment. In particular, due to the abundance of As-bearing minerals in a wide range of ore types, many buildings worldwide are potentially significantly contaminated with As even though few are directly related to As production or handling. Characterizing the secondary As mineralspecies present at mine and mineralprocessing sites is critical in understanding the potentialheal th risk these sites might pose.

Mineralogical-chemical techniques (XRD, SEM/EDX, WDXRF) and a sequential selective extraction procedure were applied to mine-waste materials and stream sediments from the Baccu Locci stream catchment (Sardinia, Italy) affected by serious As contamination as a consequence of past mining. Results indicate that solid-state speciation of As is mainly dominated by the presence of Fe(III) hydroxides (arsenical ferrihydrites with various Fe/As molar ratios) occurring as coatings of silicate grains, in which As is contained as sorbed or co-precipitated species. Scorodite (FeAsO4·2H2O) is common too, whereas arsenopyrite is generally subordinate but, owing to its relatively rapid oxidation, environmentally significant. Moreover, some unidentified arsenates of Ca-Fe or K-Fe were also detected. Arsenic contained in these phases is slowly, but continuously, released in relatively small amounts through three main mechanisms: (1) oxidation of residual arsenopyrite to scorodite; (2) decomposition of scorodite into a hydroxide or oxide of Fe(III); (3) desorption/release from Fe(III) hydroxides. Decomposition of the unidentified arsenates is also probable, e.g. Ca-Fe arsenate → calcite + Fe(III) hydroxide + As release. The flotation tailings are widely scattered and distributed in the middle–lower Baccu Locci stream catchment, and represent the most dangerous As-generating contamination source in the study area.

Microwave dielectric heating methods for the preparation of a number of arsenate, phosphate, vanadate, molybdate and carbonate minerals and their deuterated analogues are reported; rapid and efficient syntheses of these have been achieved. The application of this to the study of vibrational spectroscopy of minerals is discussed, with particular reference to scorodite.

The new mineral tooeleite occurs with pyrite, arsenopyrite, scorodite, and jarosite at the U.S. Mine, Tooele Country, Utah. Analysis by electron microprobe gave Fe2O3 43.56%, As2O5 38.61%, SO3 7.24%, and H2O by the Penfield method 9.80%. For this analysis, the suggested formula is Fe8-2x3+[(AS1-xSx)O4]6(OH)6.5H20; x is about 0.2.Crystals are orthorhombic, perhaps Pbcm or Pbc21, with a = 6.416, b 19.45, c = 8.941 Å. The strongest diffraction lines are [d in Å, (hkl), (I)] 9.75 (020) (10); 3.208 (200,132) (9); 3.047 (061,220) (5); 4.476 ({002) (4) and 2.680 (240,113) (4). The mineral is optically negative with a small 2V; α = 1.94, β = 2.05, γ = 2.06. Hardness = 3, Dmeas = 4.23, Dcalc = 4.15 g/cm3 for Z = 2.

Scorodite from Kiura mine, Bungo, Japan, has been known for many years. However, owing to its diversity in crystallographical and optical properties as well as chemical composition from those of other localities there appears to be some doubts as to the identity of the mineral. It has even been suggested to be possibly a new mineral having a composition akin to that of scorodite. Some time ago a number of fine crystals were placed at our disposal by the courtesy of Dr. Kô, in addition to the recent acquisition by our Institute of a few rarely found beautiful druses of the mineral. It will therefore be worth while to describe some of its main features in detail.

At Terras mine there is an interesting junction of a well-marked tin-bearing elvan, whose course is about north and south, with a bed of greenstone, whose general bearing is nearly east and west. Near the junction, a few years since, a shaft was sunk 40 fathoms deep for the purpose of working a tin lode which was believed to cross the elvan just refered to at that point. At a depth of about 10 fathoms the bed of greenstone was met with, and it continued for 6 fathoms in depth in a very hard state, but from thence to the bottom of shaft it was much softer.The rock is one of the hardest and toughest I have ever come across. Ordinarily it is composed of a fine-grained mixture of hornblende and silica, but it contains numerous narrow cavities or partial fissures, which near the shaft in question are often studded over or lined with small crystals of the three arseniates mentioned above.