Moctezumit

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Moctezumit
Moctezumite-75947.jpg
Moctezumite from the type locality "Moctezuma Mine", Moctezuma (Sonora) , Mexico (image width 4 mm)
General and classification
other names

IMA 1965-004

chemical formula Pb (UO 2 ) (TeO 3 ) 2
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.JK.65 ( 8th edition : IV / G.02d)
01/34/05/01
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  = 7.81  Å ; b  = 7.06 Å; c  = 13.77 Å
β  = 93.7 °
Formula units Z  = 4
Physical Properties
Mohs hardness ≈ 3
Density (g / cm 3 ) measured: 5.73; calculated: 7.256
Cleavage completely after {100}
colour light to dark orange, brownish orange
Line color not defined
transparency translucent
shine frosted
radioactivity very strong

Moctezumite is a very rare mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the monoclinic crystal system with the chemical composition Pb (UO 2 ) (TeO 3 ) 2 and is therefore chemically a lead - uranyl - tellurite .

Moctezumite is translucent and develops crystals only a few millimeters in size with a tabular, leafy habit and rounded crystal surfaces. Its color varies from light and dark orange to brownish orange. Its Mohs hardness of around 3 corresponds to that of the reference mineral calcite , which means that the mineral can be scratched with a copper coin.

Etymology and history

Moctezumite was first discovered in the gold mine “La Bambolla” (also Moctezuma Mine ) near Moctezuma in the Mexican state of Sonora and described in 1965 by Richard V. Gaines, who named the mineral after its type of locality .

Type material of the mineral is stored under catalog number 175.84 in the Mines ParisTech ( École des mines ) in Paris , France and in the National Museum of Natural History in Washington, DC under catalog numbers 128392, 164345, 164364.

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the moctezumite belonged to the department of " arsenites , selenites , tellurites and iodates ", where together with Guilleminit it formed the "guilleminit-moctezumite group. With UO 2 “and the other members Demesmaekerit and Guilleminit formed.

In the last revised and updated Lapis mineral directory by Stefan Weiß in 2018 , which, out of consideration for private collectors and institutional collections, is still based on this classic system of Karl Hugo Strunz , the mineral was given the system and mineral number. IV / K.03-20 . In the “Lapis system” this corresponds to the section “ Sulphites , Selenites and Tellurites”, where Moctezumite only forms an independent but unnamed group together with Schmitterite .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and was updated by the International Mineralogical Association (IMA) until 2009, classifies moctezumite in the expanded division of " Antimonites , bismuthites , sulfites, selenites and tellurites". This is further subdivided according to the possible presence of additional anions and / or water of crystallization , so that the mineral is classified according to its composition in the sub-section of “Tellurites without additional anions; without H 2 O “is to be found, where it is the only member of the unnamed group 4.JK.65 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns moctezumite to the class of "sulfates, chromates and molybdates", but also to the category of "selenites, tellurites and sulfites". Here he is to be found as the only member in the unnamed group 01/34/05 within the subdivision of " Selenites - Tellurites - Sulphites with A 2+ XO 3 ".

Crystal structure

Moctezumite crystallizes monoclinically in the space group P 2 1 / c (space group no. 14) with the lattice parameters a  = 7.81  Å ; b  = 7.06 Å; c  = 13.77 Å and β = 93.7 ° and 4 formula units per unit cell . Template: room group / 14

properties

The mineral is radioactive due to its uranium content of up to 28.7% . Taking into account the proportions of the radioactive elements in the idealized empirical formula and the Folgezerfälle of the natural decay chains a specific activity of about 51.432 k for the mineral Bq stated / g (compared to natural potassium 0.0312 kBq / g). The quoted value can vary significantly depending on the mineral content and the composition of the levels; selective enrichment or depletion of the radioactive decay products is also possible and changes the activity.

Education and Locations

Moctezumit forms as a rare secondary mineral in the oxidation zone of hydrothermal gold - tellurium - deposits . As Begleitminerale occur among others barite , Burckhardtit , Emmonsit , pyrite , Schmitterit , zemannite and limonite limonite on.

The previously (as of 2013) known site is its type locality "La Bambolla" near Moctezuma.

Precautions

Due to the strong radioactivity of the mineral, mineral samples from Moctezumit should only be kept in dust- and radiation-proof containers, but especially never in living rooms, bedrooms or workrooms. Absorption into the body ( incorporation , ingestion ) should also be prevented in any case and, for safety, direct body contact should be avoided and face masks and gloves should be worn when handling the mineral.

See also

literature

  • Richard V. Gaines: Moctezumite, a new lead uranyl tellurite . In: American Mineralogist . tape 50 , 1965, pp. 1158–1163 (English, minsocam.org [PDF; 371 kB ; accessed on September 23, 2019]).
  • George H. Swihart, Pradip K. Sen Gupta, Elmer O. Schlemper, Malcolm E. Back, Richard V. Gaines: The crystal structure of moctezumite [PbUO 2 ] (TeO 3 ) 2 . In: American Mineralogist . tape 78 , 1993, p. 835–839 (English, minsocam.org [PDF; 601 kB ; accessed on September 23, 2019]).

Web links

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

Individual evidence

  1. ↑ a b c d e 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.  277 (English).
  2. ^ A b David Barthelmy: Moctezumite Mineral Data. In: webmineral.com. Retrieved September 23, 2019 .
  3. ↑ George H. Swihart, Pradip K. Sen Gupta, Elmer O. Schlemper, Malcolm E. Back, Richard V. Gaines: The crystal structure of moctezumite [PbUO 2 ] (TeO 3 ) 2 . In: American Mineralogist . tape 78 , 1993, p. 836 (English, minsocam.org [PDF; 601 kB ; accessed on September 23, 2019]).
  4. ↑ a b Moctezumite . 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 September 23, 2019]).
  5. ↑ Catalog of Type Mineral Specimens - M. (PDF 124 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed August 29, 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 September 23, 2019 .
  8. ^ Moctezumite. In: mindat.org. Hudson Institute of Mineralogy, accessed September 23, 2019 .