Fineness

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Fineness
Feinglosite.jpg
Yellowish finelosite crystals from the open pit "Vouves", Thasos (see Thasos (Mining and Metal Extraction) ), Greece
General and classification
other names

IMA 1995-013

chemical formula
  • Pb 2 (Zn, Fe) [(As, S) O 4 ] 2 · H 2 O
  • Pb 2 (Zn, Fe 2+ ) (AsO 4 , SO 4 ) 2 (OH, H 2 O)
  • Pb 2 (Zn, Fe 2+ ) [(OH, H 2 O) (AsO 4 , SO 4 ) 2 ]
  • Pb 2 Zn (AsO 4 ) 2 · H 2 O
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		8.BG.05 ( 8th edition : VII / B.24)
02/40/08/03
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic sphenoid; 2 or monoclinic prismatic; 2 / m
Space group P 2 1 (No. 4) or P 2 1 / m (No. 11)Template: room group / 4Template: room group / 11
Lattice parameters a  = 8.973  Å ; b  = 5.955 Å; c  = 7.766 Å
β  = 112.20 °
Formula units Z  = 2
Physical Properties
Mohs hardness Vickers hardness VHN 100 = 263 kg / mm 2 , corresponds to a Mohs hardness of 4-5
Density (g / cm 3 ) 6.52 (calculated), 6.56 (calculated)
Cleavage not specified
Break ; Tenacity not specified; cuttable
colour pale olive green, yellow, yellow green
Line color White
transparency transparent
shine Diamond luster
Crystal optics
Optical character biaxial (optical orientation unknown)

Feinglosite is a very rarely occurring mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the monoclinic crystal system with the chemical formula Pb 2 (Zn, Fe) [(As, S) O 4 ] 2 · H 2 O, so it is chemically a water-containing lead - zinc - arsenate - sulfate and the Zn-dominant analogue of arsenic brace bushit .

Feinglosite forms radiant spherical aggregates , which mostly have a goethite core. In addition, there are individual aggregates up to 0.5 mm in diameter, which consist of very small crystallites 5 - 10 µm in length. The mineral was found in a 2 cm diameter cavity in the massive chalcosine ore in the Tsumeb Mine, Namibia.

Etymology and history

In 1984 Mark N. Feinglos gave a specimen containing solid chalcosine, which filled a cavity with pale olive-colored aggregates from an unknown mineral, to AM Clark of the Natural History Museum, London, for identification. All that is known about the origin of the stage is that it was found “sometime in the 1970s”. Originally mistaken for Heyit, microprobe analyzes showed that it was a lead-zinc arsenate. Further investigations led to the determination of the presence of a new mineral which was recognized under the number "IMA 1995-013" in 1995 by the International Mineralogical Association (IMA) and in 1997 by a British-Canadian research team with AM Clark and Alan J. Criddle from Natural History Museum , London , Andrew C. Roberts and Maurizio Bonardi from the Geological Survey of Canada , Ottawa , as well as Elizabeth A. Moffatt from the Canadian Conservation Institute, Ottawa, in the scientific journal "Mineralogical Magazine" as a fine lot.

The mineral was named after the American medical researcher and mineral collector Mark N. Feinglos (* 1948) from Durham , North Carolina / USA , who discovered the mineral, who specialized in Tsumeb minerals .

The type material is kept at the Natural History Museum , London , (Collection No. BM 1984,943) and at Harvard University , Cambridge , Massachusetts (Catalog No. 95.66).

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the fine loosite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the division of "anhydrous phosphates with foreign anions ", where it together with arsenic brackebuschit , arsenic sumebite , bearthite , Brackebuschit , Bushmakinit , Calderónit , Gamagarit , Goedkenit , Jamesit , Lulzacit , Tokyoit and tsumebite the "Brackebuschit group" with the system number. VII / B.24 .

The 9th edition of Strunz's mineral systematics, which has been in force since 2001 and is used by the International Mineralogical Association (IMA), assigns the fine glosite to the class of "phosphates, arsenates and vanadates" and there to the department of "phosphates etc. with additional anions; without H 2 O “. However, this section is further subdivided according to the size of the cations involved and their molar ratio to the phosphate, arsenate or vanadate complex, so that the mineral can be classified in the sub-section “With medium-sized and large cations; (OH etc.): RO 4  = 0.5: 1 “is to be found, where together with arsenic brackebuschite, arsentsumebit, bearthite, brackebuschite, bushmakinite, calderónite, gamagarit, Goedkenit, Tokyoit and tsumebit the“ brackebuschite group ”with the System no. 8.BG.05 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , also assigns the finite to the class of "phosphates, arsenates and vanadates", but there in the department of "water-containing phosphates etc.". Here it forms within the subdivision of “ water-containing phosphates etc., with A 2+ (B 2+ ) 2 (XO 4 ) × x (H 2 O) ” together with brackish bushite, arsenic brace bushite, feinglosite and bushmakinite also the “ brackebuschite group “With the system no. 02/40/08 .

Chemism

Mean values ​​from seven microprobe analyzes on finesite from Tsumeb led to contents of 61.4% PbO, 7.3% ZnO, 1.8% FeO, 22.1% As 2 O 5 , 5.3% SO 3 and 2.1% H 2 O (calculated from the difference). This resulted in the empirical formula Pb 2.09 (Zn 0.68 Fe 2+ 0.18 ) Σ = 0.86 [(As 0.73 , S 0.25 ) Σ = 0 (based on eight anions ) , 98 O 4 ] 2 · H 1.76 O, which has been simplified to Pb 2 (Zn, Fe) [(As, S) O 4 ] 2 · H 2 O. The type level is an iron and sulphate-rich variety of the Feinlosite.

Feinglosite is the Zn-dominant analog of the Fe 3+ -dominated arsenic brackebuschite, Pb 2 Fe 3+ (AsO 4 ) 2 (OH). Both are representatives of the brackish bushite group of M 2+ -M 3+ -oxy salts (phosphates, arsenates, vanadates, sometimes with sulfate contents) with the general formula M 2+ 2 M 3+ (TO 4 ) 2 (OH), in the for M 2+ = Ca, Ba, Sr, Ba and for M 3+ = Al, Fe and Mn (sometimes also medium-sized to small M 2+ cations such as Zn 2+ , Fe 2+ , Cu 2+ ). Feinglosit is the only representative with a water molecule in its ideal formula.

Crystal structure

Finelosite crystallizes monoclinically in the space group P 2 1 (space group no. 4) or in the space group P 2 1 / m (space group no. 11) with the lattice parameters a  = 8.973  Å ; b  = 5.955 Å; c  = 7.766 Å and β = 112.20 ° and two formula units per unit cell . Template: room group / 4 Template: room group / 11

Feinglosite has structural similarities and similarities with the other minerals of the brackish bushite group. A description of the structure for Feinglosite does not yet exist.

properties

morphology

In the "Tsumeb Mine", fine losite forms spherical to kidney-shaped aggregates with radial rays, which usually have a core of goethite. There are also individual aggregates up to 0.5 mm in diameter, which consist of very small crystallites of 5 to 10 µm in length. From the “Christiana Mine”, fine losite is only known in the form of pseudomorphoses .

physical and chemical properties

The aggregates and crystallites of the fineness are pale olive green, their line color , however, is always white. The surfaces of the transparent crystals show a distinct diamond-like sheen .

In the reflected light (bevel), the fine limestone is very pale brownish-gray and has a significantly lower reflectivity than the goethite that has grown together with it. Internal reflexes are common; they are colorless in the absence of goethite and very pale yellow if there are inclusions of goethite in the fineness. Reflective pleochroism is absent. Finesite is not noticeably anisotropic. Its bireflectance is very weak, but measurable.

No cleavage was found in the crystals of the fines . Feinglosite has a Vickers hardness of VHN 100  = 253–283 kg / mm 2 (mean value 263 kg / mm 2 ), which corresponds to a Mohs hardness of 4–5, and is therefore one of the medium-hard minerals that are similar to the reference mineral fluorite ( Hardness 4) and apatite (hardness 5) scratch more or less easily with the pocket knife.

Like solid copper , fines can be cut. Measured values ​​for the density of the fine granite do not exist, the calculated density for the mineral is 6.56 g / cm³.

Education and Locations

As a very rare mineral formation, finelosite could only be described by two sites 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 . The exact location within the Tsumeb Mine is not known. A second location is in the "Christiana Mine" near Agios Konstandinos (St. Constantin, Kamariza) not far from Lavrion , Attica , Greece . Another site known so far only from an analyzed sample is the Vouves opencast mine on the Greek island of Thasos (see Thasos (mining and metal extraction) ).

Fine losite occurs as a typical secondary formation in the complex Cu-Pb-Zn ore deposits of the “Tsumeb Mine” , which are located in carbonate rocks. Lead, zinc, iron, arsenic and sulfur come from the decomposition of former sulfidic ore minerals. At the type level, finelosite is accompanied by chalkosin and goethite as well as wulfenite and angelsite . A second occurrence with crystals less than 1 mm in size was found on a level with arsenic descloicite and the new, unknown lead arsenate GS 7. Finally, layers richly mineralized with fine glosite have been found on material which probably originates from the 3rd oxidation zone. The tiny, yellow crystals are typically fused with plaster of paris.

From the "Christiana Mine" one knows finelosite in yellow-green pseudomorphoses after idiomorphic scorodite crystals, after needle-like adamin - olivite and after Thometzekit . The former adamin / olivite needles are up to 2 mm long and have a diameter of up to 0.3 mm, while the pseudomorphosed scorodite aggregates are up to 4 mm in size. A number of the examined "Feinglosit" samples of different training (pseudomorphic and crusts) and tints has, however, without exception Chenevixit proved.

use

Feinglosite is only of interest to mineral collectors due to its rarity.

See also

literature

  • Feinglosit , 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 )
  • AM Clark, Alan J. Criddle, Andrew C. Roberts, Maurizio Bonardi, Elizabeth A. Moffatt: Feinglosite, a new mineral related to brackebuschite, from Tsumeb, Namibia . In: Mineralogical Magazine . tape 61 , 1997, pp. 285–289 ( rruff.info [PDF; 311 kB ]).

Web links

Commons : Feinglosite  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d e f g h i j k l m AM Clark, Alan J. Criddle, Andrew C. Roberts, Maurizio Bonardi, Elizabeth A. Moffatt: Feinglosite, a new mineral related to brackebuschite, from Tsumeb, Namibia . In: Mineralogical Magazine . tape 61 , 1997, pp. 285–289 ( rruff.info [PDF; 311 kB ]).
  2. ↑ a b c Feinglosit , 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 )
  3. ^ 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.  454 .
  4. ↑ Mindat - mineral description Feinglosit
  5. ^ A b Joseph A. Mandarino: Abstracts of New Mineral Descriptions (Department) . In: The Mineralogical Record . tape 28 , 1997, pp. 483-486 .
  6. ↑ a b Georg Gebhard: Tsumeb . 1st edition. GG Publishing, Grossenseifen 1999, p. 294 + 323 .
  7. ↑ a b c Branko Rieck: Rare arsenates from the Kamariza and other new finds from Lavrion . In: Lapis . 24 (issue 7/8), 1999, p. 68-76 .
  8. ↑ Catalog of Type Mineral Specimens - F. (PDF 73 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed August 29, 2019 .
  9. ↑ a b Mindat - Description of the Brackebuschitgruppe
  10. ↑ Mindat - Number of localities for Feinglosit
  11. ↑ a b List of locations for Biehlite in the Mineralienatlas and Mindat
  12. ↑ Commons image description: Yellowish crystals of the extremely rare mineral feinglosite associated to also yellowish helmutwinklerite, both minerals typical of Tsumeb, but in this case from Vouves, Thasos Island, Macedonia Department, Greece. Both in a matrix of massive adamine. Specimen analyzed by SEM / EDS
  13. ↑ Georg Gebhard: Tsumeb . 1st edition. GG Publishing, Reichshof 1991, p. 226 .
  14. ↑ Joachim Gröbner, Uwe Kolitsch: New finds by Laurion from 2001 and 2002 . In: The opening . tape 53 , 2002, p. 363-371 .