Cumengeit

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Cumengeit
Cumengite.jpg
Cumengeit crystals from the "Amelia Mine" near Santa Rosalía (Mexico)
General and classification
chemical formula Pb 21 Cu 20 (OH) 40 Cl 42 • 6H 2 O
Mineral class
(and possibly department) 		Halides
System no. to Strunz
and to Dana 		3.DB.20 ( 8th edition : III / D.12)
06/10/07/01
Crystallographic Data
Crystal system tetragonal
Crystal class ; symbol ditetragonal-dipyramidal; 4 / m 2 / m 2 / m
Space group I 4 / mmm
Lattice parameters a  = 15.065  Å ; c  = 24.436 Å
Formula units Z  = 2
Physical Properties
Mohs hardness 2.5
Density (g / cm 3 ) 4.66
Cleavage good after {101}; clearly after {110}; indistinct after {001}
colour indigo blue
Line color sky blue
transparency translucent
shine Glass gloss
Crystal optics
Refractive indices n ω  = 2.026 to 2.041
n ε  = 1.926 to 1.965
Birefringence δ = 0.100
Optical character uniaxial negative

Cumengeit (occasionally also cumengite ) is a very rarely occurring mineral from the mineral class of halides . It crystallizes in the tetragonal crystal system with the chemical composition Pb 21 Cu 20 (OH) 40 Cl 42 · 6H 2 O and develops tetragonal, pyramidal crystals of indigo blue color.


Etymology and history

Cumengeit was first described in 1893 by François Ernest Mallard , who named the mineral after Edouard Cumenge , a French mineralogist and mining engineer. The spelling of the name was defined by Burke in 2008. The designation as Cumengéit (with acute ), however, is incorrect.

classification

In the old (8th edition) and the new systematics of minerals according to Strunz (9th edition) , the cumengeit belongs to the department of oxyhalides (and related double halides). However, the new Strunz mineral classification now subdivides more precisely according to the cations involved in the formula and the mineral is accordingly in the sub-section “With Pb, Cu, etc.”.

The systematics of minerals according to Dana also assigns the Cumengeit to the oxyhalides, but according to the classification according to chemical composition in the subdivision "Oxyhalides and hydroxyhalides with the formula A m B n (O, OH) p X q " .

Education and Locations

Cumengeit forms as a typical secondary mineral in the oxidation zone of lead - copper - deposits . Individual crystals with a pseudo- octahedral or pseudo-cubo-octahedral appearance are rarely found . Oriented adhesions ( epitaxy ) of cubic boleit or pseudoboleit and pyramidal cumene geit are much more common . The "Amelia Mine" near Santa Rosalía in Mexico represents the type locality of these three minerals, where the largest crystals with a diameter of about 3.5 cm have been found so far.

Accompanying minerals , in addition to the intergrowth partners already mentioned, include atacamite , anglesite , cerussite , gypsum and phosgenite .

In addition to its type locality, the mineral could also be detected worldwide at the following, a total of 36 sites (status: 2009), namely Broken Hill , Clarendon (South Australia) , Penguin (Tasmania) and Ashburton Downs / Pilbara (Shire of Ashburton) in Australia; near Goslar and Lautenthal (Lower Saxony) and in the coal mining area of Essen (North Rhine-Westphalia) in Germany; at Laurion in Greece; on Vesuvius , near Varenna , Villaputzu and in the province of Livorno in Italy; near Nandraž / Revúca (Okres) in Slovakia; at Vegadeo in Spain; in several locations in the British regions of England and Wales ; at Painted Rock in the Carrizo Plain National Monument of Arizona (USA).

Crystal structure

Cumengeit crystallizes in the tetragonal crystal system in the space group I 4 / mmm with the lattice parameters a = 15.065  Å and c = 24.436 Å as well as two cell parameters per unit cell .

See also

Individual evidence

  1. ↑ a b c Webmineral - Cumengite (English)
  2. ↑ a b American Mineralogist Crystal Structure Database - Cumengeite (English, 1986)
  3. ↑ a b c Cumengeite at mindat.org (English)
  4. ↑ IMA / CNMNC List of Mineral Names (2009) - Cumengeite (English; PDF 1.8 MB; p. 67)
  5. ↑ Mindat - Localities of Cumengeite
  6. ↑ American Mineralogist Crystal Structure Database - Cumengeite (English, 1986)

literature

  • Cumengeite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 67.8 kB )
  • Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp. 496 .
  • Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 70 .

Web links

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