Marcus J. Origlieri

On the mineralogy of the “Anthropocene Epoch”

Abstract The “Anthropocene Epoch” has been proposed as a new post-Holocene geological time interval—a period characterized by the pervasive impact of human activities on the geological record. Prior to the influence of human technologies, the diversity and distribution of minerals at or near Earth’s surface arose through physical, chemical, and/or biological processes. Since the advent of human mining and manufacturing, particularly since the industrial revolution of the mid-eighteenth century, mineral-like compounds have experienced a punctuation event in diversity and distribution owing to the pervasive impact of human activities. We catalog 208 mineral species approved by the International Mineralogical Association that occur principally or exclusively as a consequence of human processes. At least three types of human activities have affected the diversity and distribution of minerals and mineral-like compounds in ways that might be reflected in the worldwide stratigraphic record. The most obvious influence is the widespread occurrence of synthetic mineral-like compounds, some of which are manufactured directly for applications (e.g., YAG crystals for lasers; Portland cement) and others that arise indirectly (e.g., alteration of mine tunnel walls; weathering products of mine dumps and slag). A second human influence on the distribution of Earth’s near-surface minerals relates to large-scale movements of rocks and sediments—sites where large volumes of rocks and minerals have been removed. Finally, humans have become relentlessly efficient in redistributing select natural minerals, such as gemstones and fine mineral specimens, across the globe. All three influences are likely to be preserved as distinctive stratigraphic markers far into the future.

The crystal structure of bartelkeite, with a revised chemical formula, PbFeGeVI(Ge2IVO7)(OH)2·H2O, isotypic with high-pressure P21/m lawsonite

Abstract Bartelkeite from Tsumeb, Namibia, was originally described by Keller et al. (1981) with the chemical formula PbFeGe3O8. By means of electron microprobe analysis, single-crystal X-ray diffraction, and Raman spectroscopy, we examined this mineral from the type locality. Our results show that bartelkeite is monoclinic with space group P21/m, unit-cell parameters a = 5.8279(2), b = 13.6150(4), c = 6.3097(2) Å, β = 127.314(2)°, and a revised ideal chemical formula PbFeGeVIGe2IVO7(OH)2·H2O (Z = 2). Most remarkably, bartelkeite is isostructural with the high-pressure P21/m phase of lawsonite, CaAl2Si2O7(OH)·H2O, which is only stable above 8.6 GPa and a potential host for H2O in subducting slabs. Its structure consists of single chains of edge-sharing FeO6 and Ge1O6 octahedra parallel to the c-axis, cross-linked by Ge22O7 tetrahedral dimers. The average bond lengths for the GeO6 and GeO4 polyhedra are 1.889 and 1.744 Å, respectively. The Pb atoms and H2O groups occupy large cavities within the framework. The hydrogen bonding scheme in bartelkeite is similar to that in lawsonite. Bartelkeite represents the first known mineral containing both 4- and 6-coordinated Ge atoms and may serve as an excellent analog for further exploration of the temperature-pressure-composition space of lawsonite.

Agardite-(Y), Cu2+6Y(AsO4)3(OH)6·3H2O

Agardite-(Y), with a refined formula of Cu2+ 5.70(Y0.69Ca0.31)[(As0.83P0.17)O4]3(OH)6·3H2O [ideally Cu2+ 6Y(AsO4)3(OH)6·3H2O, hexacopper(II) yttrium tris(arsenate) hexahydroxide trihydrate], belongs to the mixite mineral group which is characterized by the general formula Cu2+ 6 A(TO4)3(OH)6·3H2O, where nine-coordinated cations in the A-site include rare earth elements along with Al, Ca, Pb, or Bi, and the T-site contains P or As. This study presents the first structure determination of agardite-(Y). It is based on the single-crystal X-ray diffraction of a natural sample from Jote West mine, Pampa Larga Mining District, Copiapo, Chile. The general structural feature of agardite-(Y) is characterized by infinite chains of edge-sharing CuO5 square pyramids (site symmetry 1) extending down the c axis, connected in the ab plane by edge-sharing YO9 polyhedra (site symmetry -6..) and corner-sharing AsO4 tetrahedra (site symmetry m..). Hydroxyl groups occupy each corner of the CuO5-square pyramids not shared by a neighboring As or Y atom. Each YO9 polyhedron is surrounded by three tubular channels. The walls of the channels, parallel to the c axis, are six-membered hexagonal rings comprised of CuO5 and AsO4 polyhedra in a 2:1 ratio, and contain free molecules of lattice water.

Redetermination of despujolsite, Ca3Mn4+(SO4)2(OH)6·3H2O

The crystal structure of despujolsite [tricalcium manganese bis(sulfate) hexahydroxide trihydrate], the Ca/Mn member of the fleischerite group, ideally Ca3Mn4+(SO4)2(OH)6·3H2O, was previously determined based on X-ray diffraction intensity data from photographs, without H-atom positions located [Gaudefroy et al. (1968 ▶). Bull. Soc. Fr. Minéral. Crystallogr. 91, 43–50]. The current study redetermines the structure of despujolsite from a natural specimen, with all H atoms located and with higher precision. The structure of despujolsite is characterized by layers of CaO8 polyhedra (m.. symmetry) interconnected by Mn(OH)6 octahedra (32. symmetry) and SO4 tetrahedra (3.. symmetry) along [001]. The average Ca—O, Mn—O and S—O bond lengths are 2.489, 1.915, and 1.472 Å, respectively. There are two distinct hydrogen bonds that stabilize the structural set-up. This work represents the first description of hydrogen bonds in the fleischerite group of minerals.

Schaurteite, Ca3Ge(SO4)2(OH)6·3H2O

This report presents the first crystal structure determination of the mineral schaurteite, ideally Ca3Ge(SO4)2(OH)6·3H2O, tricalcium germanium bis(sulfate) hexahydroxide trihydrate. This single-crystal X-ray diffraction study investigated a natural sample from the type locality at Tsumeb, Namibia. Schaurteite is a member of the fleischerite group of minerals, which also includes fleischerite, despujolsite, and mallestigite. The structure of schaurteite consists of slabs of Ca(O,OH,H2O)8 polyhedra (site symmetry mm2) interleaved with a mixed layer of Ge(OH)6 octahedra (-3m.) and SO4 tetrahedra (3m.). There are two H atoms in the asymmetric unit, both located by full-matrix refinement, and both forming O—H⋯O hydrogen bonds.

Pirquitasite, Ag(2)ZnSnS(4).

Pirquitasite, ideally Ag2ZnSnS4 (disilver zinc tin tetrasulfide), exhibits tetragonal symmetry and is a member of the stannite group that has the general formula A2BCX 4, with A = Ag, Cu; B = Zn, Cd, Fe, Cu, Hg; C = Sn, Ge, Sb, As; and X = S, Se. In this study, single-crystal X-ray diffraction data are used to determine the structure of pirquitasite from a twinned crystal from the type locality, the Pirquitas deposit, Jujuy Province, Argentina, with anisotropic displacement parameters for all atoms, and a measured composition of (Ag1.87Cu0.13)(Zn0.61Fe0.36Cd0.03)SnS4. One Ag atom is located on Wyckoff site Wyckoff 2a (symmetry -4..), the other Ag atom is statistically disordered with minor amounts of Cu and is located on 2c (-4..), the (Zn, Fe, Cd) site on 2d (-4..), Sn on 2b (-4..), and S on general site 8g. This is the first determination of the crystal structure of pirquitasite, and our data indicate that the space group of pirquitasite is I-4, rather than I-42m as previously suggested. The structure was refined under consideration of twinning by inversion [twin ratio of the components 0.91 (6):0.09 (6)].

New data on hemihedrite from Arizona

Abstract Hemihedrite from the Florence Lead-Silver mine in Pinal County, Arizona, USAwas first described and assigned the ideal chemical formula Pb10Zn(CrO4)6(SiO4)2F2, based upon a variety of chemical and crystalstructure 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 PO4 and 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 fromthe Rat Tail claim, Arizona, indicate that hemihedrite is triclinic in space group P1, 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 single-crystal X-ray diffraction data to R1 = 0.022 for 5705 unique observed reflections, and the ideal chemical formula Pb10Zn(CrO4)6(SiO4)2(OH)2 was assumed during the refinement. Electron microprobe analyses of this sample yielded the empirical chemical formula Pb10.05(Zn0.91Mg0.02)Σ = 0.93(Cr5.98S0.01P0.01)Σ = 6.00 Si1.97O34H2.16 based on 34 O atoms and six (Cr + S + P) per unit cell.

Redetermination of ruizite,Ca2Mn3+2[Si4O11(OH)2](OH)2.2H2O

The crystal structure of ruizite, ideally Ca2Mn3+ 2[Si4O11(OH)2](OH)2·2H2O was redetermined based on single-crystal X-ray diffraction data of a natural sample from the Wessels mine, Northern Cape Province, South Africa, in space group C2. All non-H atoms were refined with anisotropic displacement parameters and all hydrogen atoms were located, improving upon previous results and yielding a significantly lower R factor.