Ojuelait

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Ojuelait
Ojuelaite-167693.jpg
Ojuelait from the Christiana Mine, Agios Konstantinos, Lavrio District (Attica), Greece (field of view 4 mm)
General and classification
other names
  • IMA 1979-035
  • Ojuélite
chemical formula
  • ZnFe 3+ 2 (AsO 4 ) 2 (OH) 2 · 4H 2 O
  • ZnFe 3+ 2 [OH | AsO 4 ] 2 • 4H 2 O
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.DC.15
11.42.18.03
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / c (No. 14)Template: room group / 14
Lattice parameters a  = 10.24  Å ; b  = 9.66 Å; c  = 5.56 Å
β  = 94.4 °
Formula units Z  = 2
Physical Properties
Mohs hardness 3
Density (g / cm 3 ) measured and calculated: 3.39
Cleavage after {010}
colour yellowish green
Line color light yellow
transparency translucent
shine Glass gloss, silk gloss
Crystal optics
Refractive indices n α  = 1.696
n β  = 1.730
n γ  = 1.798
Birefringence δ = 0.102
Optical character biaxial positive
Axis angle 2V = 73 ° (measured); 74 ° (calculated)

Ojuelaite is a very rare mineral from the mineral class of "phosphates, arsenates and vanadates". It crystallizes in the monoclinic crystal system with the chemical composition ZnFe 3+ 2 [OH | AsO 4 ] 2 · 4H 2 O, so it is chemically a water-containing zinc - iron - arsenate with hydroxide ions as additional anions .

Ojuelait is translucent and has a yellowish green color with a light yellow streak color . The mineral only develops small, fibrous to needle-like crystals a few millimeters in size, which are usually arranged in radial tufts. The crystal surfaces themselves have a glass-like sheen , while fibrous aggregate forms show a soft shimmer similar to silk .

With a Mohs hardness of 3, Ojuelaite is one of the medium-hard minerals that, like the reference mineral calcite, can be scratched with a copper coin.

Etymology and history

The mineral was first discovered in the Ojuela Mine near Mapimí in the Mexican state of Durango and described in 1981 by Fabien Cesbron, Miguel Romero Sanchez and Sidney A. Williams, who named it after its type locality .

The type material of the mineral is kept in the University of Pierre and Marie Curie in Paris and in the National Museum of Natural History in Washington (Catalog No. 145679).

classification

Ojuelait is not listed in the outdated 8th edition of the Strunz mineral classification . Only in the most recently revised and updated Lapis mineral directory by Stefan Weiß, which, out of consideration for private collectors and institutional collections, is still based on this classic systematics by Karl Hugo Strunz , was the mineral given the system and mineral number. VII / D.08-50 . In the "Lapis Classification" corresponds to the class of "phosphates, arsenates and vanadates" and then the department "water containing phosphates, with foreign anions " where Ojuelait with Arthurit , Bendadait , Cobaltarthurit , Coralloit , Earlshannonit , Kleemanit , Kunatit , Mapimit and Whitmoreit the "Arthurit-Gruppe" with the system no. VII / D.08 forms.

The 9th edition of Strunz's mineral systematics, valid since 2001 and updated by the International Mineralogical Association (IMA) until 2009, also assigns ojuelaite to the category of “phosphates, etc. with additional anions; with H 2 O “. However, this is further subdivided according to the relative size of the cations and the molar ratio of the additional anions to the phosphate, arsenate or vanadate complex (RO 4 ), so that the mineral can be classified in the sub-section “With only medium-sized cations; (OH etc.): RO 4  = 1: 1 and <2: 1 "can be found, where together with arthurite, bendadaite, cobalt arthurite, earlshannonite, kunatite and whitmoreit the" Whitmoreit group "with the system no. 8.DC.15 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns ojuelaite to the class of "phosphates, arsenates and vanadates" and there to the category of "water-containing phosphates etc., with hydroxyl or halogen". Here he is also in the " Whitmoreit group " with system no. 11/22/18 within the subsection “Water-containing phosphates etc., with hydroxyl or halogen with (AB) 4 (XO 4 ) 3 Z q × x (H 2 O)”.

Crystal structure

Ojuelait crystallizes monoclinically in the space group P 2 1 / c (space group no. 14) with the lattice parameters a  = 10.24  Å ; b  = 9.66 Å; c  = 5.56 Å and β = 94.4 ° and two formula units per unit cell . Template: room group / 14

Education and Locations

Ojuelait formed in the oxidation zone of arsenic-rich and polymetallic, hydrothermal ore - deposits . At its type locality and so far the only known site in Mexico, the Ojuela mine, the mineral occurred in paragenesis with paradamite , scorodite , smithsonite and limonite .

Other previously known sites are the Tsumeb Mine in Namibia, where the mineral appeared in association with smithsonite and tennantite and goethite ; some pits at Agios Konstantinos and Hilarion in the Greek parish of Lavrio (Attica) and the Sterling mine at Sterling Hill in Sussex County of the US state New Jersey.

See also

literature

  • Fabien Cesbron, Miguel Romero Sanchez, Sidney A. Williams: Mapimite and ojuelaite, two new hydrated arsenates of zinc and iron, from the Ojuela mine Mapimi, Mexico . In: Bulletin de Minéralogie . tape 104 , 1981, pp. 582-586 (English).
  • Michael Fleischer , Louis J. Cabri, GY Chao, JA Mandarino, Adolf Pabst : New Mineral Names . In: American Mineralogist . tape 67 , 1982, pp. 621–624 (English, available online at rruff.info [PDF; 545 kB ; accessed on May 5, 2019]).
  • John M. Hughes, Erich S. Bloodaxe, Kyle D. Kobel: The atomic arrangement of ojuelaite, ZnFe 3+ 2 (AsO 4 ) 2 (OH) 2 · 4H 2 0 . In: Mineralogical Magazine . tape 60 , June 1996, p. 519–521 (English, [1] [PDF; 180 kB ; accessed on May 5, 2019]).

Web links

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

Individual evidence

  1. ↑ a b Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: March 2019. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, March 2019, accessed May 20, 2019 .
  2. ↑ a b c d e f Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  498 (as  Ojuélite ) .
  3. ↑ a b Ojuelaite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 68  kB ; accessed on May 5, 2019]).
  4. ↑ a b c Ojuelaite. In: mindat.org. Hudson Institute of Mineralogy, accessed May 5, 2019 .
  5. ^ Catalog of Type Mineral Specimens - Ojuelaite. (PDF 36 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed May 5, 2019 .
  6. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  7. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed April 25, 2019 .
  8. ↑ Find location list for Ojuelaite at the Mineralienatlas and at Mindat