ALBERT

Description: The new mineral anorpiment, As2S3, the triclinic dimorph of orpiment, has space group P1I and cell parameters a = 5.7577(2), b = 8.7169(3), c = 10.2682(7) Å, a = 78.152(7), ß = 75.817(7), ? = 89.861(6)°, V = 488.38(4) Å3 and Z = 4. It occurs at the Palomo mine, Castrovirreyna Province, Huancavelica Department, Peru. It is a low-temperature hydrothermal mineral associated with dufrénoysite, muscovite, orpiment, pyrite and realgar. It occurs in drusy crusts of wedge-shaped, transparent, greenish yellow crystals. The streak is yellow. The lustre is resinous on crystal faces, but pearly on cleavage surfaces. The Mohs hardness is about 1. The mineral is sectile with an irregular fracture and one perfect and easy cleavage on {001}. The measured and calculated densities are 3.33 and 3.321 g cm-3, respectively. All indices of refraction are greater than 2. The mineral is optically biaxial (–) with 2V = 35–40° and no observed dispersion. The acute bisectrix (X) is approximately perpendicular to the {001} cleavage. Electron microprobe analyses yielded the averages and ranges in wt.%: As 58.21 (57.74–59.03), S 38.72 (38.33 39.00), total 96.94 (96.07 97.75), providing the empirical formula (based on 5 atoms) As1.96S3.04. The strongest powder X-ray diffraction lines are [d (hkl) I] 4.867(002) 97, 4.519 (110,11I1) 77, 3.702 (1I1I1) 46, 3.609 (022,11I2) 82, 2.880 (201,02I2,1I2I1,023) 75, 2.552 (1I13,1I31,132) 100, 2.469 (114,130,13I1) 96. The structure of anorpiment [R1 = 0.021 for 1484 reflections with Fo 〉 4s(F)] consists of layers of covalently bonded As and S atoms. Each S atom bonds to two As atoms at As–S–As angles between 100.45 and 104.15°. Each As atom is strongly bonded to three S atoms at S–As–S angles between 91.28 and 103.59°, forming an AsS3 pyramid with As at its apex. The As–S linkages within the layers form rings of six AsS3 pyramids. Interlayer bonding forces are interpreted as van der Waals. The structure of anorpiment is similar to that of orpiment in that it is composed of layers of As2S3 macromolecules, but arranged in a different stacking sequence.

Description: The crystal structure and chemical composition of two samples of fettelite from the type locality, including a portion of the holotype material, was investigated to verify if a previously proposed revision of the chemical formula was applicable, and to study the role of cation substitution for Hg that would suggest new members of the fettelite family. The crystal structure of fettelite from the type locality was found to be equivalent to that reported previously for the Chilean occurrence, and consists of an alternation of two kinds of layers along c: layer A with general composition [Ag6As2S7]2− and layer B with general composition [Ag10HgAs2S8]2+. In this structure, the Ag atoms occur in various coordination configurations, varying from quasi-linear to quasi-tetrahedral, the AsS3 groups form pyramids as are typically observed in sulfosalts, and Hg links two sulfur atoms in a linear coordination. The refined compositions for the crystals in this study, [Ag6As2S7][Ag10(Fe0.53Hg0.47)As2S8] (R100124) and [Ag6As2S7][Ag10(Hg0.79Cu0.21)As2S8] (R110042), clearly indicate that new mineral species related to fettelite are likely to be found in nature.

Description: Hemihedrite from the Florence Lead-Silver mine in Pinal County, Arizona, USA was first described and assigned the ideal chemical formula Pb 10 Zn(CrO 4 ) 6 (SiO 4 ) 2 F 2 , based upon a variety of chemical and crystal-structure analyses. The primary methods used to determine the fluorine content for hemihedrite were colorimetry, which resulted in values of F that were too high and inconsistent with the structural data, and infrared (IR) spectroscopic analysis that failed to detect OH or H 2 O. Our reinvestigation using electron microprobe analysis of the type material, and additional samples from the type locality, the Rat Tail claim, Arizona, and Nevada, reveals the absence of fluorine, while the presence of OH is confirmed by Raman spectroscopy. These findings suggest that the colorimetric determination of fluorine in the original description of hemihedrite probably misidentified F due to the interferences from PO 4 and SO 4 , both found in our chemical analyses. As a consequence of these results, the study presented here proposes a redefinition of the chemical composition of hemihedrite to the ideal chemical formula Pb 10 Zn(CrO 4 ) 6 (SiO 4 ) 2 (OH) 2 . Hemihedrite is isotypic with iranite with substitution of Zn for Cu, and raygrantite with substitution of Cr for S. Structural data from a sample from the Rat Tail claim, Arizona, indicate that hemihedrite is triclinic in space group P 1 , a = 9.4891(7), b = 11.4242(8), c = 10.8155(7) Å, α = 120.368(2)°, β = 92.017(3)°, = 55.857(2)°, V = 784.88(9) Å 3 , Z = 1, consistent with previous investigations. The structure was refined from single-crystal X-ray diffraction data to R 1 = 0.022 for 5705 unique observed reflections, and the ideal chemical formula Pb 10 Zn(CrO 4 ) 6 (SiO 4 ) 2 (OH) 2 was assumed during the refinement. Electron microprobe analyses of this sample yielded the empirical chemical formula Pb 10.05 (Zn 0.91 Mg 0.02 ) = 0.93 (Cr 5.98 S 0.01 P 0.01 ) = 6.00 Si 1.97 O 34 H 2.16 based on 34 O atoms and six (Cr + S + P) per unit cell.

Description: Hydroxycalciomicrolite, Ca 1.5 Ta 2 O 6 (OH) is a new microlite-group mineral found in the Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil. It occurs as isolated octahedral and as a combination of octahedral and rhombic dodecahedral crystals, up to 1.5 mm in size. The crystals are yellow and translucent, with a white streak and vitreous to resinous lustre. The mineral is brittle, with a Mohs hardness of 5–6. Cleavage is not observed and fracture is conchoidal. The calculated density is 6.176 g cm –3 . Hydroxycalciomicrolite is isotropic, n calc. = 2.010. The infrared and Raman spectra exhibit bands due to O–H stretching vibrations. The chemical composition determined from electron microprobe analysis ( n = 13) is (wt.%): Na 2 O 0.36(8), CaO 15.64(13), SnO 2 0.26(3), Nb 2 O 5 2.82(30), Ta 2 O 5 78.39(22), MnO 0.12(2), F 0.72(12) and H 2 O 1.30 (from the crystal structure data), O = F –0.30, total 99.31(32), yielding an empirical formula, (Ca 1.48 Na 0.06 Mn 0.01 ) 1.55 (Ta 1.88 Nb 0.11 Sn 0.01 ) 2.00 O 6.00 [(OH) 0.76 F 0.20 O 0.04 ]. Hydroxycalciomicrolite is cubic, with unit-cell parameters a = 10.4205(1) Å, V = 1131.53(2) Å 3 and Z = 8. It represents a pyrochlore supergroup, microlite-group mineral exhibiting P 4 3 32 symmetry, instead of Fd m . The reduction in symmetry is due to long-range ordering of Ca and vacancies on the A sites. This is the first example of such ordering in a natural pyrochlore, although it is known from synthetic compounds. This result is promising because it suggests that other species with P 4 3 32 or lower-symmetry space group can be discovered and characterized.

Description: Natropalermoite, ideally Na 2 SrAl 4 (PO 4 ) 4 (OH) 4 , the Na-analogue of palermoite, is a new mineral from the Palermo No. 1 mine, Groton, New Hampshire, USA. Associated minerals are palermoite, eosphorite and quartz. Natropalermoite crystals are prismatic with striations parallel to the direction of elongation (the a axis) up to 200 μm x 50 μm x 45 μm in size. The mineral is colourless, transparent with a white streak and vitreous lustre and is visually indistinguishable from palermoite. It is brittle with subconchoidal fracture and has a Mohs hardness of 5.5. Cleavage is perfect on {001}, fair on {100} and no parting was observed. The calculated density is 3.502 g cm –3 . Natropalermoite is biaxial (–), α = 1.624(1), β = 1.641(1), = 1.643(1) (589 nm), 2V meas = 43(4) o , 2V calc = 38 o . An electron microprobe analysis yielded an empirical formula (based on 20 O apfu) of (Na 1.69 Li 0.31 ) 2.00 (Sr 0.95 Mg 0.04 Ca 0.02 Ba 0.01 ) 1.02 (Al 3.82 Mn 0.03 Fe 0.03 ) 3.88 (P 1.01 O 4 ) 4 (OH) 4 . Natropalermoite is orthorhombic, space group Imcb , a = 11.4849(6), b = 16.2490(7), c = 7.2927(4) Å, V = 1360.95(17) Å 3 , Z = 4. Natropalermoite is isotypic with palermoite, but substitution of the larger Na for Li results in substantial increase of the b cell parameter. Four of the seven Na–O distances are longer than their equivalents in palermoite, resulting in a more regular 7-fold coordination polyhedron about Na. The eight strongest peaks in the calculated X-ray powder diffraction are [ d calc (Å), I rel %, ( hkl )]: [3.128, 100, (321)], [4.907, 68, (121)], [3.327, 48, (022)], [4.689, 45, (220)], [3.078, 45, (202)], [2.453, 38, (242)], [2.636, 35, (411)], [2.174, 35, (422)].

Description: Hemihedrite from the Florence Lead-Silver mine in Pinal County, Arizona, USA was first described and assigned the ideal chemical formula Pb10Zn(CrO4)6(SiO4)2F2, based upon a variety of chemical and crystal-structure analyses. The primary methods used to determine the fluorine content for hemihedrite were colorimetry, which resulted in values of F that were too high and inconsistent with the structural data, and infrared (IR) spectroscopic analysis that failed to detect OH or H2O. Our reinvestigation using electron microprobe analysis of the type material, and additional samples from the type locality, the Rat Tail claim, Arizona, and Nevada, reveals the absence of fluorine, while the presence of OH is confirmed by Raman spectroscopy. These findings suggest that the colorimetric determination of fluorine in the original description of hemihedrite probably misidentified F due to the interferences from PO4and SO4, both found in our chemical analyses. As a consequence of these results, the study presented here proposes a redefinition of the chemical composition of hemihedrite to the ideal chemical formula Pb10Zn(CrO4)6(SiO4)2(OH)2. Hemihedrite is isotypic with iranite with substitution of Zn for Cu, and raygrantite with substitution of Cr for S. Structural data from a sample from the Rat Tail claim, Arizona, indicate that hemihedrite is triclinic in space groupP1,a= 9.4891(7),b= 11.4242(8),c= 10.8155(7) Å, α = 120.368(2)°, β = 92.017(3)°, γ = 55.857(2)°,V= 784.88(9) Å3,Z= 1, consistent with previous investigations. The structure was refined from singlecrystal X-ray diffraction data toR1= 0.022 for 5705 unique observed reflections, and the ideal chemical formula Pb10Zn(CrO4)6(SiO4)2(OH)2was assumed during the refinement. Electron microprobe analyses of this sample yielded the empirical chemical formula Pb10.05(Zn0.91Mg0.02)∑ = 0.93(Cr5.98S0.01P0.01)∑ = 6.00Si1.97O34H2.16based on 34 O atoms and six (Cr + S + P) per unit cell.

Description: Hydroxycalciomicrolite, Ca1.5Ta2O6(OH) is a new microlite-group mineral found in the Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil. It occurs as isolated octahedral and as a combination of octahedral and rhombic dodecahedral crystals, up to1.5 mm in size. The crystals are yellow and translucent, with a white streak and vitreous to resinous lustre. The mineral is brittle, with a Mohs hardness of 5–6. Cleavage is not observed and fracture is conchoidal. The calculated density is 6.176 g cm–3. Hydroxycalciomicroliteis isotropic,ncalc.= 2.010. The infrared and Raman spectra exhibit bands due to O–H stretching vibrations. The chemical composition determined from electron microprobe analysis (n= 13) is (wt.%): Na2O 0.36(8), CaO 15.64(13), SnO20.26(3),Nb2O52.82(30), Ta2O578.39(22), MnO 0.12(2), F 0.72(12) and H2O 1.30 (from the crystal structure data), O = F –0.30, total 99.31(32), yielding an empirical formula, (Ca1.48Na0.06Mn0.01)∑1.55(Ta1.88Nb0.11Sn0.01)∑2.00O6.00[(OH)0.76F0.20O0.04].Hydroxycalciomicrolite is cubic, with unit-cell parametersa= 10.4205(1) Å,V= 1131.53(2) Å3andZ= 8. It represents a pyrochlore supergroup, microlite-group mineral exhibitingP4332 symmetry, instead ofFd3m. Thereduction in symmetry is due to long-range ordering of Ca and vacancies on theAsites. This is the first example of such ordering in a natural pyrochlore, although it is known from synthetic compounds. This result is promising because it suggests that other species withP4332or lower-symmetry space group can be discovered and characterized.

Description: The crystal structure and chemical composition of two samples of fettelite from the type locality, including a portion of the holotype material, was investigated to verify if a previously proposed revision of the chemical formula was applicable, and to study the role of cation substitution for Hg that would suggest new members of the fettelite family. The crystal structure of fettelite from the type locality was found to be equivalent to that reported previously for the Chilean occurrence, and consists of an alternation of two kinds of layers along c: layer A with general composition [Ag6As2S7]2– and layer B with general composition [Ag10HgAs2S8]2+. In this structure, the Ag atoms occur in various coordination configurations, varying from quasi-linear to quasi-tetrahedral, the AsS3 groups form pyramids as are typically observed in sulfosalts, and Hg links two sulfur atoms in a linear coordination. The refined compositions for the crystals in this study, [Ag6As2S7][Ag10(Fe0.53Hg0.47)As2S8] (R100124) and [Ag6As2S7][Ag10(Hg0.79Cu0.21)As2S8] (R110042), clearly indicate that new mineral species related to fettelite are likely to be found in nature.

Description: The new mineral anorpiment, As2S3, the triclinic dimorph of orpiment, has space group PI and cell parameters a = 5.7577(2), b = 8.7169(3), c = 10.2682(7) Å, α = 78.152(7), β = 75.817(7), γ = 89.861(6)°, V = 488.38(4) Å3 and Z = 4. It occurs at the Palomo mine, Castrovirreyna Province. Huancavelica Department, Peru. It is a low-temperature hydrothermal mineral associated with dufrenoysite, muscovite, orpiment, pyrite and realgar. It occurs in drusy crusts of wedge-shaped, transparent, greenish yellow crystals. The streak is yellow. The lustre is resinous on crystal faces, but pearly on cleavage surfaces. The Mohs hardness is about VA. The mineral is sectile with an irregular fracture and one perfect and easy cleavage on ﹛001﹜. The measured and calculated densities are 3.33 and 3.321 g cm–3, respectively. All indices of refraction are greater than 2. The mineral is optically biaxial (—) with 2V = 35—40° and no observed dispersion. The acute bisectrix (X) is approximately perpendicular to the ﹛001﹜ cleavage. Electron microprobe analyses yielded the averages and ranges in wt.%: As 58.21 (57.74–59.03), S 38.72 (38.33–39.00), total 96.94 (96.07–97.75), providing the empirical formula (based on 5 atoms) As1.96S3.04. The strongest powder X-ray diffraction lines are [d (hkl) I] 4.867(002) 97, 4.519 (110,11̄1) 77, 3.702 (1̄1̄1) 46, 3.609 (022,11̄2) 82, 2.880(201,02̄2,1̄2̄1,023) 75, 2.552 (1̄13,1̄31,132) 100, 2.469 (114,130,13̄1) 96. The structure of anorpiment [R1 = 0.021 for 1484 reflections with F0 〉 4σ(F)] consists of layers of covalently bonded As and S atoms. Each S atom bonds to two As atoms at As—S—As angles between 100.45 and 104.15°. Each As atom is strongly bonded to three S atoms at S—As—S angles between 91.28 and 103.59°, forming an AsS3 pyramid with As at its apex. The As—S linkages within the layers form rings of six AsS3 pyramids. Interlayer bonding forces are interpreted as van der Waals. The structure of anorpiment is similar to that of orpiment in that it is composed of layers of As2S3 macromolecules, but arranged in a different stacking sequence.