Jamesite

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Jamesite
Jamesite-177450.jpg
Red-brown Jamesite crystals, accompanied by tsumcorite, fragranceite and goethite, from the Tsumeb mine in Namibia (step size: 4.3 cm × 3.5 cm × 2.8 cm)
General and classification
other names

IMA 1978-079

chemical formula
  • Pb 2+ 2 ZnFe 3+ 2 (Fe 3+ 2.8 Zn 1.2 ) (AsO 4 ) 4 (OH) 8 [(OH) 1.2 O 0.8 ]
  • Pb 2 Zn 2 (Fe 3+ , Zn) 5 [(OH, O) 10 | (AsO 4 ) 4 ]
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.BK.25 ( 8th edition : VII / B.24)
11.11.02.01
Similar minerals Ludlockite , carminite (weathered), arseniosiderite , goethite
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 5.583  Å ; b  = 9.542 Å; c  = 10.219 Å,
α  = 109.81 °; β  = 90.57 °; γ  = 97.71 °
Formula units Z  = 1
Frequent crystal faces {010}, {100}, {001}
Physical Properties
Mohs hardness ≈ 3
Density (g / cm 3 ) 5.084 (calculated)
Cleavage not observed
Break ; Tenacity not specified; not specified
colour red-brown
Line color light brown
transparency translucent
shine Semi-diamond luster
Crystal optics
Refractive indices n α  = 1.960
n β  = 1.995
n γ  = 2.020
Refractive index n  = 1.992 (measured), 1.989 (calculated)
Birefringence δ = 0.060
Optical character biaxial negative
Axis angle 2V = 75 °
Pleochroism strong from X = light brown through Y = light brown to Z = deep red brown
Other properties
Chemical behavior sparingly soluble in hot HCl and HNO 3

Jamesite is a very rarely occurring mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the triclinic crystal system with the chemical formula Pb 2+ 2 ZnFe 3+ 2 (Fe 3+ 2.8 Zn 1.2 ) (AsO 4 ) 4 (OH) 8 [(OH) 1.2 O 0.8 ] , is chemically a lead - zinc - iron arsenate with additional hydroxide ions .

According to {010}, Jamesite forms tabular and elongated crystals according to [100] up to 0.5 mm in length as well as spherical aggregates with a radial structure. The mineral was first found - along with tsumcorite , fragranceite and goethite - in corroded lead ore in the Tsumeb Mine, Namibia.

Etymology and history

Red-brown Jamesite from the Tsumeb Mine in Namibia (step size: 3 cm × 3 cm × 2.5 cm)

The German mineral collector Wolfgang Bartelke , who noticed the mineral in 1979 among other specimens from Tsumeb, is considered to be the discoverer of Jamesite . Corresponding investigations led to the determination of the presence of a new mineral, which was recognized by the International Mineralogical Association (IMA) in 1978 and published in 1981 by a German-American research team with Paul Keller , Heinz Hess and Pete J. Dunn in the science magazine "Chemie der Erde". as Jamesite was described. The mineral was named after the English mining engineer Christopher James, who was commissioned in 1900 by the Otavi Mining and Railway Company (OMEG) to continue the exploration work begun by Mathew Rogers in Tsumeb. James, leader of a 33-strong group, reached Tsumeb on August 13, 1900. By March 14, 1901, his people had sunk a 38 m deep shaft and were starting to drive exploratory sections. With these sections of 18 m and 48 m in length, the horizontal extension of the Tsumeb ore tube could be contoured. On August 13, 1901, James was finally able to give a first, preliminary report - which ultimately led to the investigated occurrence of copper and lead ores as the "Tsumeb Mine" being in production for nine decades.

The type material is available at the University of Stuttgart under the collection no. TM 78.79-8910.20 at the site 0/824-s27 / 2 (Mineral stage, 2 x 2 x 0.5 cm and single crystal in Mark tubes) and in the Smithsonian Institution belonging to National Museum of Natural History , Washington, DC (catalog no. 143955, Cotyp), kept.

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the jamesite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the department of "anhydrous phosphates with foreign anions ", where together with arsenic brackebuschit , arsenic sumebite , bearthite , Brackebuschit , Bushmakinit , Calderónit , Feinglosit , Gamagarit , Goedkenit , Lulzacit , Tokyoit and Tsumebit the "Brackebuschit-Gruppe" with the system no. VII / B.24 .

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns Jamesite to the category of “phosphates etc. with additional anions; without H 2 O “. However, this is further subdivided according to the relative size of the cations involved and the molar ratio of the additional anions (OH etc.) to the phosphate, arsenate or vanadate complex (RO 4 ), so that the mineral can be classified in the sub-section “With medium-sized and large cations; (OH etc.): RO 4  = 2: 1, 2.5: 1 ”is to be found, where the“ Jamesite group ”with the system no. 8.BK.25 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Jamesite to the class of "phosphates, arsenates and vanadates" and there to the category of "anhydrous phosphates, etc., with hydroxyl or halogen". Here he is to be found as the only member of the unnamed group 41.11.02 within the sub-section “Anhydrous phosphates etc., with hydroxyl or halogen with different formulas”.

Chemism

Mean values ​​from microprobe analyzes on jamesite from Tsumeb resulted in traces of copper, manganese and sulfur in contents of 27.1% PbO, 11.1% ZnO, 25.5% Fe 2 O 3 and 36.2% As 2 O 5 . This resulted in the empirical formula Pb 1.92 Zn 2.15 Fe 3+ 5.06 O 4 (As 4.98 O 20 ), which was idealized to Pb 2 Zn 2 Fe 3+ O 4 (AsO 4 ) 5 , which requires levels of 28.2% PbO, 10.3% ZnO, 25.2% Fe 2 O 3 and 36.2% As 2 O 5 .

Years later, considerations of crystal chemistry led to this chemical composition being questioned. Average values ​​from two microprobe analyzes resulted in contents of 27.40% PbO, 10.39% ZnO, 23.30% Fe 2 O 3 , 27.94% As 2 O 3 , 0.27% Ga 2 O 3 , 0.09% Al 2 O 3 , 0.21% CuO and 5.06% H 2 O (calculated), from which the empirical formula with Pb 2.01 Zn 1.00 Fe 3+ 2.00 (Fe 3+ 2.78 Zn 1 , 09 Ga 0.05 Cu 0.04 Al 0.03 ) Σ = 3.99 (AsO 4 ) 3.99 [(OH) 9.20 O 0.80 ] Σ = 10.00 . An idealization leads to Pb 2+ 2 (Fe 3+ 4.8 Zn 2.2 ) (AsO 4 ) 4 (OH) 8 [(OH) 1.2 O 0.8 ]. However, since three of the M positions are completely ordered [ M (1) = Zn, M (2) = Fe 3+ , M (3) = Fe 3+ ], the formula is written as follows to better understand the features of the crystal structure to represent: Pb 2+ 2 Zn (Fe 3+ 2 (Fe 3+ 2.8 Zn 1.2 ) (AsO 4 ) 4 (OH) 8 [(OH) 1.2 O 0.8 ].

The two formulas (from 1981 and from 1999) differ significantly, in particular there are considerable differences in the contents of As 2 O 5 and H 2 O. The older formula also did not take the hydroxide ions into account.

Crystal structure

Jamesite crystallizes triclinically in the space group P 1 (space group no. 2) with the lattice parameters a  = 5.583  Å ; b  = 9.542 Å; c  = 10.219 Å; α = 109.81 °; β = 90.57 ° and γ = 97.71 ° and one formula unit per unit cell . Template: room group / 2

Compact trimers of edge-sharing Zn [6] - and Fe [6] - octahedra share edges with adjacent trimers and form so [M 3 (OH, O) 10 ] chains parallel z [100] -As. B. also in Kotoit , Lindgrenit and Frankhawthorneit -, and are decorated by AsO 4 - tetrahedron . Parallel to these chains there are ladder-like structures, which consist of linear trimers of edge-sharing octahedra, which are connected by AsO 4 tetrahedra. The chains and ladders are linked by octahedra, which share corners with the octahedra in the chains and ladders, and by the AsO 4 tetrahedra to form a parallel layer (010). The layers in turn are connected in the direction [010] and in this way form a heteropolar framework with large gaps in which the Pb [7] ions sit.

properties

morphology

Jamesite forms lath-shaped crystals that are extremely thin tabular according to {010} and stretched in the direction of the a-axis [100]. Only the pinacoids {100} and {001} have been identified in other forms. The Jamesite crystals, which are sometimes intergrown subparallel, reach sizes of up to 0.5 mm × 0.2 mm × 0.05 mm. Furthermore, there are spherical to wart-shaped aggregates with a radial structure.

physical and chemical properties

Jamesite crystals are red-brown in color, but their streak color is always light brown. The surfaces of the translucent crystals show a clear semi-diamond-like sheen , which agrees well with the very high birefringence of the mineral (δ = 0.060).

No cleavage was found in the Jamesite crystals . The mineral has a Mohs hardness of ≈ 3 and is therefore one of the medium-hard minerals that, like the reference mineral calcite, can be easily scratched with a copper coin. Measured values ​​for the density of the Jamesite do not exist, the calculated density for the mineral is 5.084 g / cm³.

Jamesite is sparingly soluble in hot hydrochloric acid HCl and nitric acid HNO 3 .

Education and Locations

Jamesite occurs as a typical secondary formation in the heavily corroded lead ore of complex Cu-Pb-Zn deposits in carbonate rocks. Lead, zinc, iron and arsenic come from the decomposition of former sulphidic ore minerals such as galena , sphalerite and tennantite . Jamesite occurs together with a lot of fragranceite, tsumcorite, goethite and very little secondary dolomite . All minerals form more or less porous masses, which were found in heavily corroded lead ore. The age sequence of paragenesis with Jamesite is: Duftite I → Tsumcorite → Goethite → Jamesite → Duftite II → Dolomite. It is a variant of the widespread Paragenesis I / 1 by Tsumeb with scentite, cerussite, goethite and dolomite. Fragrance I, tsumcorite and goethite always occur in granular or radial masses, fragrance II and dolomite always in idiomorphic crystals. If fragrance II occurs only sparsely, then Jamesite is also idiomorphic. If Jamesite forms spherical aggregates with a radial structure, which are encrusted by Duftite II, it can easily be overlooked due to its similarity to Goethite.

As a very rare mineral formation, Jamesite could only be described from three sites so far (as of 2016). The type locality of the Jamesite is one of the two upper oxidation zones (probably the second oxidation zone) of the world-famous Cu-Pb-Zn-Ag-Ge-Cd deposit of the "Tsumeb Mine" (Tsumcorp Mine) in Tsumeb , Oshikoto Region , Namibia . The exact location within the Tsumeb Mine is not known.

The second site in the world for jamesite - here with a clear copper content - was the Bakara mine in carbonates in the Balkans (Stara Planina), Wraza Oblast , Bulgaria .

A third location is in the "Christiana Mine" (shaft No. 132 or Christiana 132) near Agios Konstandinos (St. Constantin, Kamariza) not far from Lavrion , Attica , Greece . Jamesite was only found here in inconspicuous formations together with scentite and goethite on a fine-grain quartz matrix.

use

Due to its rarity, Jamesite is only of interest to mineral collectors.

See also

literature

  • Jamesite. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001 ( PDF, 66 kB )
  • Mark A. Cooper, Frank Christopher Hawthorne : Local Pb 2+ - □ disorder in the crystal structure of jamesite, Pb 2 ZnFe 3+ 2 (Fe 3+ 2.8 Zn 1.2 ) (AsO 4 ) 4 (OH) 8 [(OH) 1.2 O 0.8 ], and revision of the chemical formula . In: The Canadian Mineralogist . tape 37 , 1999, pp. 53–60 ( rruff.info [PDF; 769 kB ]).
  • Paul Keller, Heinz Hess, Pete J. Dunn: Jamesite, Pb 2 Zn 2 Fe 3+ 5 O 4 (AsO 4 ) 5 , a new mineral from Tsumeb, Namibia . In: Chemistry of the Earth . tape 40 , 1981, pp. 105-109 .

Web links

Individual evidence

  1. ↑ a b c d e f g Mark A. Cooper, Frank Christopher Hawthorne : Local Pb 2+ - □ disorder in the crystal structure of jamesite, Pb 2 ZnFe 3+ 2 (Fe 3+ 2.8 Zn 1.2 ) (AsO 4 ) 4 (OH) 8 [(OH) 1.2 O 0.8 ], and revision of the chemical formula . In: The Canadian Mineralogist . tape 37 , 1999, pp. 53–60 ( rruff.info [PDF; 769 kB ]).
  2. ^ A b Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  461 .
  3. ↑ a b c d e f g h i j k Paul Keller, Heinz Hess, Pete J. Dunn: Jamesite, Pb 2 Zn 2 Fe 3+ 5 O 4 (AsO 4 ) 5 , a new mineral from Tsumeb, Namibia . In: Chemistry of the Earth . tape 40 , 1981, pp. 105-109 .
  4. ^ Gerhard Söhnge: Tsumeb - a historical scetch (Scientific research in South West Africa 5th series) . 2nd Edition. Publisher of the SWA Scientific Society, Windhoek 1976, OCLC 258175481 .
  5. ^ Type mineral catalog Germany - storage of the holotype stage Jamesite
  6. ↑ Catalog of Type Mineral Specimens - J. (PDF 40 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed August 29, 2019 .
  7. ↑ Paul Keller: Tsumeb / Namibia - one of the most spectacular mineral discovery sites on earth . In: Lapis . 9 (issue 7/8), 1984, p. 13-63 .
  8. ↑ Mindat - mineral description Jamesite
  9. ↑ Jamesite. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001 ( PDF, 66 kB )
  10. ^ Paul Keller: Paragenesis . In: The Mineralogical Record . 8 (Volume 3), 1977, p. 38-47 .
  11. ↑ Mindat - Number of localities for Jamesite
  12. ↑ a b c List of places where Jamesite was found in the Mineralienatlas and Mindat
  13. ↑ Georg Gebhard: Tsumeb . 1st edition. GG Publishing, Reichshof 1991, ISBN 3-925322-02-7 , pp. 173 .
  14. ↑ Georg Gebhard: Tsumeb . 1st edition. GG Publishing, Grossenseifen 1999, ISBN 3-925322-03-5 , pp. 250 + 322 .
  15. ↑ Jordanka Minčeva-Stefanova: Arsenate minerals diversity in oxidation zones of the polymetallic stratabound deposits in Western Balkan Mountain . In: Comptes Rendus de l'Academie Bulgare des Sciences . tape 54 , 2001, p. 39-42 , bibcode : 2001CRABS..54f..39M .
  16. ↑ Branko Rieck: Rare arsenates from the Kamariza and other new finds from Lavrion . In: Lapis . 24 (issue 7/8), 1999, p. 68-76 .