Plumboselite
| Plumboselite | |
|---|---|
| General and classification | |
| other names |
|
| chemical formula | Pb 3 O 2 (SeO 3 ) |
|
Mineral class (and possibly department) |
Oxides (hydroxides, V [5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates) |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-pyramidal; mm 2 |
| Space group | Cmc 2 1 (No. 36) |
| Lattice parameters | a = 10.5384 Å ; b = 10.7452 Å; c = 5.7577 Å |
| Formula units | Z = 4 |
| Frequent crystal faces | {010} |
| Physical Properties | |
| Mohs hardness | 2 to 3 |
| Density (g / cm 3 ) | 7.814 (calculated) |
| Cleavage | none observed |
| Break ; Tenacity | brittle; not specified |
| colour | colorless |
| Line color | White |
| transparency | transparent |
| shine | matt (dull) to diamond gloss |
| Crystal optics | |
| Refractive index | n = 2.115 |
| Optical character | biaxial, optical orientation cannot be determined |
| Axis angle | 2V = cannot be determined |
Plumboselite is a very rarely occurring mineral from the mineral class of the " oxides and hydroxides " (including the V [5,6] vanadates, arsenites, antimonites, bismutites, sulfites, selenites, tellurites and iodates). It crystallizes in the orthorhombic crystal system with the chemical formula Pb 3 O 2 (SeO 3 ), so it is chemically a lead selenite with additional oxygen atoms .
At the time of the first description, only three levels with plumboselite were known. The mineral then forms sub-parallel to divergent-rayed aggregates of thin, parallel [001] elongated and {010} platy crystals with a maximum length of 0.3 mm, but which do not exceed 5 μm wide and 2 μm thick. The plumboselite sits on top of Clausthalite and was found in the Tsumeb Mine , Namibia.
Etymology and history
The Australian mineralogist John Innes (? –1992), chief mineralogist of the Tsumeb Corporation in the late 1970s, who recovered the mineral in the "Tsumeb Mine", is considered to be the discoverer of plumboselite . It was mentioned in 1999 as a Pb-Se mineral under the name "GS 19".
"The rare element selenium has been found in the minerals umangite and clausthalite. The latter forms tiny crystals in an altered dolomite. The clausthalite crystals are covered by the only known selenate from Tsumeb, GS 19, still under investment. "
“The rare element selenium was found in the minerals umangite and clausthalite. The latter forms tiny crystals in an altered dolomite. The Clausthalite crystals are coated with the only selenate known from Tsumeb, GS 19, which is still in the research stage. "
The mineral that was misidentified as selenate turned out to be selenite in the course of the investigations in which it became clear that a new mineral is present. After completion of the scientific investigations, the mineral was recognized in 1997 by the International Mineralogical Association (IMA) under the number "IMA 1997-023" and in 1999 by Anthony R. Kampf of the Natural History Museum of Los Angeles County in Los Angeles, Stuart J. Mills from the University of British Columbia in Vancouver , and William W. Pinch from Pittsford in the science magazine "Mineralogy and Petrology" described as plumboselite. The mineral was named after its chemical composition with lead (Latin plumbum) and the fact that it is a selenite mineral.
Type material of the mineral (the holotype) is in the collection of the Mineral Sciences Department in the Natural History Museum of Los Angeles County, Los Angeles , California / USA (catalog no. 63264).
classification
Plumboselite was only recognized as an independent mineral by the International Mineralogical Association (IMA) in 2010 and the first description was not published until 2011. A precise group assignment in the 9th edition of Strunz's mineral classification is therefore not yet known.
Chemism
Average values from seven microprobe analyzes on plumboselite resulted in contents of 0.09% CaO; 84.92% PbO and 14.95% SeO 2 . From this, the empirical formula Pb 2.92 Ca 0.01 Se 1.03 O 5 was calculated on the basis of five oxygen atoms, which was idealized to Pb 3 O 2 (SeO 3 ) and 85.78% PbO and 14.22% SeO 2 requires.
Crystal structure
Plumboselite crystallizes orthorhombically in the space group Cmc 2 1 (space group no. 36) with the lattice parameters a = 10.5384 Å ; b = 10.7452 Å and c = 5.7577 Å as well as four formula units per unit cell .
The crystal structure of plumboselite is identical to that of synthetic Pb 3 O 2 (SeO 3 ). It contains two lead atoms, one selenium atom and three oxygen atoms in an asymmetric unit. The structure is based on [O 2 Pb 3 ] double chains of oxo-centered [OPb 4 ] tetrahedra with common edges between which SeO 3 triangles sit in the direction of the c-axis [001] . The lone pairs of electrons of both the Pb 2+ atoms and the Se 4+ atoms are stereoactive.
Oxo-centered [OPb 4 ] tetrahedra can be found in countless minerals and synthetic phases . Of these, however, only twelve have [O 2 Pb 3 ] chains, and only three of them are minerals: chloroxiphite , mendipite and damaraite . Among all these phases, the crystal structure of the plumboselite is unique.
properties
morphology
Plumboselite is found in the form of subparallel to divergent-rayed aggregates consisting of thin, fiber-like crystals. The parallel [001] elongated and {010} plate-like crystals have lengths of 0.3 mm, but are never wider than 5 μm and thicker than 2 μm. Its supporting crystal form is the lateral pinacoid {010}, it is also the only surface form observed.
physical and chemical properties
Plumboselite crystals are colorless, so their streak color is always white. The surfaces of the transparent crystals can be matt or dull or have a strong diamond-like sheen , which is in accordance with the high to very high refraction of light (n = 2.115).
Neither cleavage nor divisibility was observed on the crystals of plumboselite . However , due to their brittleness, they break easily, although no statements can be made about the nature of the fracture surfaces due to the crystal size. The mineral has a Mohs hardness of 2 to 3 and is one of the soft to medium-hard minerals that, like the reference minerals plaster of paris (hardness 2), can be scratched with a fingernail or calcite (hardness 3) with a copper coin. The calculated density for plumboselite is 7.814 g / cm³.
Education and Locations
As a very rare mineral formation, plumboselite could only be described from one source so far (as of 2016). Its type locality is the world-famous Cu-Pb-Zn-Ag-Ge-Cd deposit of the "Tsumeb Mine" (Tsumcorp Mine) in Tsumeb , Oshikoto region , Namibia , where the three known stages probably in one and the same place in the late 1970s in the second oxidation zone in the area of the 30th floor have been found.
Plumboselite occurs as a typical secondary formation on corroded ores in the oxidation zone of a complex Cu-Pb-Zn deposit in carbonate rocks. Lead and selenium come from the decomposition of the primary ore mineral Clausthalite . Further accompanying minerals of plumboselenite at the three known levels are smithsonite , mimetesite and vaterite .
use
Due to its rarity, plumboselite is only of interest to mineral collectors.
See also
literature
- Anthony R. Kampf, Stuart J. Mills, William W. Pinch: Plumboselite, Pb 3 O 2 (SeO 3 ), a new oxidation-zone mineral from Tsumeb, Namibia . In: Mineralogy and Petrology . tape 101 , 2011, p. 75-80 , doi : 10.1007 / s00710-010-0137-3 .
- Plumboselite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF, 80 kB )
Web links
- Mineral Atlas: Plumboselite (Wiki)
- Mindat - Plumboselite (English)
- American-Mineralogist-Crystal-Structure-Database - Plumboselite
Individual evidence
- ↑ a b c Georg Gebhard: Tsumeb . 1st edition. GG Publishing, Grossenseifen 1999, p. 280 + 320 .
- ↑ a b c d e f g h i j k l m n o p q Anthony R. Kampf, Stuart J. Mills, William W. Pinch: Plumboselite, Pb 3 O 2 (SeO 3 ), a new oxidation-zone mineral from Tsumeb, Namibia . In: Mineralogy and Petrology . tape 101 , 2011, p. 75-80 , doi : 10.1007 / s00710-010-0137-3 .
- ↑ Mindat - Number of localities for plumboselite
- ↑ Find location list for plumboselite at the Mineralienatlas and at Mindat