Topic
Pearceite
About: Pearceite is a research topic. Over the lifetime, 30 publications have been published within this topic receiving 403 citations.
Papers
TL;DR: In this paper, the authors reported changes to the existing nomenclature for minerals belonging to the pearceite-polybasite group by means of X-ray single-crystal diffraction and electron microprobe.
Abstract: The present paper reports changes to the existing nomenclature for minerals belonging to the pearceite-polybasite group Thirty-one samples of minerals in this group from different localities, with variable chemical composition, and showing the 111, 221, and 222 unit-cell types, were studied by means of X-ray single-crystal diffraction and electron microprobe The unit-cell parameters were modeled using a multiple regression method as a function of the Ag, Sb, and Se contents The determination of the crystal structures for all the members of the group permits them to be considered as a family of polytypes and for all members to be named pearceite or polybasite The main reason for doubling the unit-cell parameters is linked to the ordering of silver The distinction between pearceite and polybasite is easily done with an electron microprobe analysis (As/Sb ratio) A hyphenated italic suffix indicating the crystal system and the cell-type symbol should be added, if crystallographic data are available Given this designation, the old names antimonpearceite and arsenpolybasite are abandoned here and the old names pearceite and polybasite, previously defined on a structural basis (ie, 111 and 222), are redefined on a chemical basis The old name pearceite will be replaced by pearceite- Tac , antimonpearceite by polybasite- Tac , arsenpolybasite-221 by pearceite- T 2 ac , arsenpolybasite-222 by pearceite- M 2 a 2 b 2 c , polybasite-221 by polybasite- T 2 ac , and polybasite-222 by polybasite- M 2 a 2 b 2 c Since all polytypes are composed of two different layers stacked along [001]: layer A, with general composition [(Ag,Cu) 6 (As,Sb) 2 S 7 ] 2− , and layer B, with general composition [Ag 9 CuS 4 ] 2+ , the chemical formulae of pearceite and polybasite should be written as [Ag 9 CuS 4 ][(Ag,Cu) 6 (As,Sb) 2 S 7 ] and [Ag 9 CuS 4 ][(Ag,Cu) 6 (Sb,As) 2 S 7 ], respectively, instead of (Ag,Cu) 16 (As,Sb) 2 S 11 and (Ag,Cu) 16 (Sb,As) 2 S 11 , as is currently accepted The new nomenclature rules were approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association
45 citations
TL;DR: In this paper, the crystal structure of the mineral pearceite, (Ag,Cu)16(As,Sb)2S11, has been solved and refined at 300, 120 and 15 K.
Abstract: The crystal structure of the mineral pearceite, (Ag,Cu)16(As,Sb)2S11, has been solved and refined at 300, 120 and 15 K. At room temperature pearceite crystallizes with trigonal symmetry, space group P\bar 3m1; the refinement of the structure leads to a residual factor of R = 0.0464 for 1109 independent observed reflections and 92 variables. The crystal structure consists of sheets stacked along the c axis. The As atoms form isolated (As,Sb)S3 pyramids, which typically occur in sulfosalts, copper cations link two S atoms in a linear coordination, and the silver cations are found in a fully occupied position and in various sites corresponding to the most pronounced probability density function locations (modes) of diffusion-like paths. These positions correspond to low-coordination (2, 3 and 4) sites, in agreement with the preference of silver for such environments. d10 silver-ion distribution has been determined by means of a combination of a Gram–Charlier description of the atomic displacement factors and a split-atom model. To analyse the crystal chemical behaviour of the silver cations as a function of temperature, a structural study was carried out at 120 K (R = 0.0450). The refinement indicates that the mineral exhibits the same structural arrangement as the room-temperature structure (space group P\overline 3m1) and shows that the silver cations are still highly disordered. In order to investigate a possible ordering scheme for the silver cations, a data collection at ultra-low temperature (15 K) was performed. The structural skeleton was found to be similar to that of the room-temperature and 120 K atomic structures, but the best solution was achieved with a fully split-atom model of five silver positions, giving an R value of 0.0449 for 651 observed reflections and 78 parameters. Although the silver cation densities condense into better defined modes, the joint probability density function still exhibits a strong overlapping of neighbouring sites.
43 citations
24 Oct 2006
TL;DR: In this article, an integrated Xthis article, DSC, CIS and EPMA study on all the members of the pearceite-polybasite group was conducted, showing that the observed structural disorder in the B layer is strongly related to the fast ion conduction character exhibited by these minerals.
Abstract: The minerals of the pearceite–polybasite group, general formula (Ag,Cu)16
M
2S11 with M = Sb, As, have been recently structurally characterized. On the whole, all the structures can be described as a regular succession of two module layers stacked along the c axis: a first module layer (labeled A), with general composition [(Ag,Cu)6(As,Sb)2S7]2−, and a second module layer (labeled B), with general composition [Ag9CuS4]2+. In detail, in the B layer of the pearceite structure silver cations are found in various sites corresponding to the most pronounced probability density function locations of diffusion-like paths. We have shown for the first time that the observed structural disorder in the B layer is strongly related to the fast ion conduction character exhibited by these minerals. This paper reports an integrated XREF, DSC, CIS and EPMA study on all the members of the pearceite–polybasite group. DSC and conductivity measurements pointed out that the 222 members show ionic-transitions at 340 K (arsenpolybasite-222) and 350 K (polybasite-222), whereas the 221 members have transitions at lower temperature, that is, 310–330 K (arsenpolybasite-221) and 335 K (polybasite-221). For the 111 members (pearceite and antimonpearceite), the transition occurs below room temperature at 273 K. In situ single-crystal X-ray diffraction experiments showed that these minerals present the same high temperature structure and are observed at room temperature either in their high temperature (HT) fast ion conductivity form or in one of the low temperature (LT) fully ordered (222), partially ordered (221) or still disordered (111) forms, with transition temperatures slightly above or below room temperature. The pearceite–polybasite group of minerals can be considered as a homogeneous series with the same aristotype, fast ion conducting form at high temperature. Depending upon the Cu content, an ordering occurs with transition temperatures related to that content: the lower the Cu content, the higher the transition temperature from the fast ion conducting HT form to the non-ion conducting form.
36 citations
Journal Article•
33 citations
TL;DR: The Kangjiawan mine as discussed by the authors is a representative hydrothermal Pb-Zn-Ag-Au deposit in the Shuikoushan district, China, which is characterized by Ag > Cu > Sb content and occurs mainly as silver minerals, such as minor argentian tetrahedrite, freibergite and abundant polybasite-arsenpolybasite, pearceite and pyrargyrite-proustite.
Abstract: The Kangjiawan deposit, in the Shuikoushan district, Hunan Province, China, is a representative hydrothermal Pb–Zn–Ag–Au deposit in this region. The orebodies consist mainly of pyritic Pb–Zn ores. Silver minerals are associated with Pb–Zn mineralization. Ag-bearing Pb–Zn ores in the deposit are characterized by Ag > Cu > Sb content. Silver occurs mainly as silver minerals, such as minor argentian tetrahedrite, freibergite and abundant polybasite–arsenpolybasite, pearceite and pyrargyrite–proustite, and all are hosted in galena. The assemblages of silver minerals found in the major orebodies change from the southern to the northern part, from argentian tetrahedrite + freibergite + pearceite + arsenpolybasite + pyrargyrite–proustite in the south to polybasite–arsenpolybasite + pyrargyrite, and to pyrargyrite in the north.
29 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2018 | 1 |
| 2015 | 3 |
| 2013 | 1 |
| 2012 | 1 |
| 2011 | 1 |
| 2008 | 1 |