Crimsonite, Pbfe23+(PO4)
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Mineralogical Magazine, October 2016, Vol. 80(6), pp. 925–935 3+ Crimsonite, PbFe2 (PO4)2(OH)2, the phosphate analogue of carminite from the Silver Coin mine, Valmy, Nevada, USA 1,* 2 3 4 A. R. KAMPF ,P.M.ADAMS ,S.J.MILLS AND B. P. NASH 1 Mineral Sciences Department, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA 2 126 South Helberta Avenue #2, Redondo Beach, California 90277, USA 3 Geosciences, Museum Victoria, GPO Box 666, Melbourne 3001, Victoria, Australia 4 Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112, USA [Received 28 May 2015; Accepted 10 September 2015; Associate Editor: Ian Graham] ABSTRACT 3þ Crimsonite (IMA2014-095), PbFe2 (PO4)2(OH)2, the phosphate analogue of carminite, is a new mineral from the Silver Coin mine, Valmy, Iron Point district, Humboldt County, Nevada, USA, where it occurs as a low-temperature secondary mineral in association with fluorwavellite, goethite, hematite, hentschelite, plumbogummite and variscite on quartz. Crimsonite occurs in subparallel aggregates of deep red blades or plates flattened on {100} and up to 0.1 mm in maximum dimension. The streak is light purplish orange. Crystals are transparent and have adamantine lustre. The Mohs hardness is ∼3½, the tenacity is brittle, the fracture is irregular to splintery and an imperfect cleavage is likely on {101}. The calculated density is 5.180 g/cm3. Crimsonite is optically biaxial (+), with 2V = 85.5(5)° and γ – α = 0.011. Using the Gladstone- Dale relationship, the calculated indices of refraction are α = 2.021, β = 2.026 and γ = 2.032. The optical orientation is X = b; Y = a; Z = c and the pleochroism is X light orange, Y light yellow, Z red brown; Y < X < Z. Electron microprobe analyses provided PbO 40.69, CaO 0.60, ZnO 0.72, CuO 0.13, Fe2O3 23.36, Al2O3 0.34, V2O5 0.70, As2O5 12.05, P2O5 16.03, SO3 0.33 and H2O 3.64 (structure), total 98.59 wt.%. The empirical formula (based on 10 O apfu) is (Pb1.06Ca0.06)Σ1.12(Fe1.71Zn0.05Al0.04Cu0.01)Σ1.81(P1.32As0.61 V0.05S0.02)Σ2.00O8[(OH)1.64(H2O)0.36]Σ2.00. Crimsonite is orthorhombic, Cccm, a = 16.2535(13), b = 7.4724(4), c = 12.1533(9) Å, V = 1476.04(17) Å3 and Z = 8. The eight strongest lines in the powder X-ray diffraction pattern are [dobs in Å(I)(hkl)]: 5.86(42)(111); 4.53(45)(112); 3.485(64)(113); 3.190(100) (022); 3.026(40)(004); 2.902(54)(511); 2.502(77)(422) and 2.268(54)(224). The structure of crimsonite (R1 = 3.57% for 740 Fo >4σF) contains FeO6 octahedra that share edges to form dimers, which are then linked to other dimers by corner sharing to form chains along [010]. These chains are linked by PO4 tetrahedra yielding sheets parallel to {001}. The sheets are linked to one another via bonds to 8-coordinated Pb2+ atoms with non-stereoactive 6s2 lone-electron pairs. K EYWORDS: crimsonite, new mineral, crystal structure, carminite, Silver Coin mine, Valmy, Nevada, USA. Introduction search of rare mineral species. To date, seven new mineral species have been described from THE Silver Coin mine, a small base-metal deposit in here: zinclipscombite (Chukanov et al., 2006), north-central Nevada (USA), was last worked, meurigite-Na (Kampf et al., 2009), iangreyite principally for silver, in 1929. Since the late 1980s, (Mills et al., 2011), krásnoite (Mills et al., 2012), the mine has been a popular site for collectors in fluorowardite (Kampf et al., 2014), ferribushma- kinite (Kampf et al., 2015b) and fluorwavellite (Kampf et al., 2015c). * E-mail: [email protected] Herein, we describe crimsonite, the seventh DOI: 10.1180/minmag.2016.080.031 new mineral species from this mine. The name is © 2016 The Mineralogical Society A. R. KAMPF ET AL. based upon the mineral’s deep red (crimson) goethite, hematite, hentschelite, plumbogummite colour and the fact that it is the phosphate and variscite on quartz. We have now confirmed analogue of carminite, a mineral with a very more than 130 mineral species from the Silver Coin similar deep red colour and whose name is also mine. The vast majority of these are from the based upon its colour (carmine). The new mineral Phosphate stope. A partial list was provided by and name have been approved by the Commission Thomssen and Wise (2004) and updates were on New Minerals, Nomenclature and Classification provided by Kampf et al. (2009, 2014, 2015) and of the International Mineralogical Association Mills et al. (2011, 2012). Adams et al. (2015) (IMA2014-095, Kampf et al., 2015a). The provide a complete, up-to-date description of the holotype specimen is housed in the collections Silver Coin mine and its mineralogy. of the Mineral Sciences Department, Natural At the Silver Coin mine, quartz veins containing History Museum of Los Angeles County, cata- argentiferous galena, sphalerite and pyrite were logue number 65558. emplaced, in part, along faults and fractures in phosphatic argillites. When exposed to vadose water, the pyrite and other sulfides were oxidized, Occurrence and paragenesis producing acidic fluids that leached PO4 and Al from the argillite wall rocks. The prolific secondary Crimsonite occurs on a single small specimen assemblage then precipitated along fractures and collected from the ceiling of the Phosphate stope at bedding planes. the Silver Coin mine, Valmy, Iron Point district, Humboldt County, Nevada, USA (40°55’44″N, Physical and optical properties 117°19’26″W). The mineral is a low-temperature secondary mineral associated with fluorwavellite, Crimsonite occurs in subparallel aggregates of blades or plates up to 0.1 mm in maximum dimension (Figs 1 and 2). The blades are flattened on {100}, somewhat elongated on [010] and exhibit the forms {100}, {101} and {011} (Fig. 3). No twinning was observed. The colour of the mineral is deep red with a slight purplish cast and it has a light purplish-orange streak. Crystals are transparent and have adamantine lustre. Crimsonite does not fluoresce in longwave or shortwave ultraviolet light. The Mohs hardness is probably ∼3½ by analogy with carminite, the tenacity is brittle and the fracture is irregular. No cleavage was observed, FIG. 1. Crimsonite crystals growing on plumbogummite FIG. 2. Electron back-scatter scanning electron micrscope that, in turn, is coating quartz. The field of view is 0.4 mm image of crimsonite crystals on plumbogummite. across. NHMLAC specimen number 65558. NHMLAC specimen number 65558. 926 CRIMSONITE, THE PHOSPHATE ANALOGUE OF CARMINITE voltage, 20 nA beam current and a beam diameter of 5–10 μm. The sample showed no visible damage under the electron beam. Raw X-ray intensities were corrected for matrix effects with a φ(ρz) (PAP) algorithm (Pouchou and Pichoir, 1991). The contents of P and As exhibited a strong negative correlation, from P/(P + As) = 0.52 to 0.79, but the variation appears to be unrelated to growth zonation, i.e. no core-to-rim variation in composition was observed. The minor contents of Vand S in the tetrahedral P site also varied, with V increasing and S decreasing with P content. There was insufficient material for CHN ana- lyses, so H2O was calculated on the basis of P + As + V + S = 2, charge balance and 10 O atoms per FIG. 3. Crystal drawing of crimsonite (clinographic projection). formula unit (apfu), as determined by the crystal structure analysis (see below). The tiny crystals do not take a good polish, which contributes to the low but an imperfect cleavage on {101} is likely by analytical total. Analytical data are given in Table 1. analogy with carminite (based on the modern cell No other elements were detected by energy-dispersive setting with a > c > b). The density could not be spectroscopy. Other probable elements were sought measured because it is greater than those of by wavelength-dispersive spectroscopy EPMA. available high-density liquids and there is insuffi- The empirical formula (based on 10 O apfu) is cient material for physical measurement. The (Pb1.06Ca0.06)Σ1.12(Fe1.71Zn0.05Al0.04Cu0.01)Σ1.81 (P1.32As0.61V0.05S0.02)Σ2.00O8[(OH)1.64(H2O)0.36]Σ2.00. calculated density based on the empirical formula 3þ and the unit cell refined from the single-crystal data The ideal formula is PbFe2 (PO4)2(OH)2, which is 5.180 g/cm3. Crimsonite is insoluble at room requires PbO 41.12, Fe2O3 29.42, P2O5 26.15 and H2O 3.32, total 100 wt.%. The structure refinement temperature in concentrated HCl and 70% HNO3. Crimsonite is optically biaxial (+). The 2V (see below) shows an extra low-occupancy large- determined from extinction data using EXCALIBR cation site near the less-than-fully-occupied octa- (Gunter et al., 2004) is 85.5(5)°. The birefringence hedral-cation site. This provides a structural basis γ – α = 0.011 was measured with a Berek compen- for the significant large-cation excess and the sator. The indices of refraction could not be significant octahedral-cation deficiency observed measured because they are higher than available in the empirical formula. index liquids; however, using the average index of refraction of 2.026 predicted by the Gladstone-Dale relationship (Mandarino, 1981), along with the X-ray crystallography and structure measured 2V and γ – α birefringence, the indices refinement of refraction can be calculated to be α = 2.021, β = 2.026 and γ = 2.032. The optical orientation is Both powder and single-crystal X-ray studies were X = b; Y = a; Z = c and the pleochroism is X light carried-out using a Rigaku R-Axis Rapid II curved orange, Y light yellow, Z red brown; Y < X < Z.