Oldhamite

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Oldhamite
Oldhamite-510145.jpg
Dark gray grains, masses and tiny veins of oldhamite in calcite from the sedimentation dump of the opencast mine Lichtenberg, Ronneburg, Thuringia ( total size : 1.5 cm × 1 cm)
General and classification
chemical formula CaS
Mineral class
(and possibly department) 		Sulfides and sulfosalts
System no. to Strunz
and to Dana 		2.CD.10 ( 8th edition : II / C.15)
08/02/01/05
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic hexakisoctahedral; 4 / m  3  2 / m
Space group Fm 3 m (No. 225)Template: room group / 225
Lattice parameters a  = 5.69  Å
Formula units Z  = 4
Physical Properties
Mohs hardness 4th
Density (g / cm 3 ) measured: 2.58; calculated: 2.589
Cleavage after {001}
colour light brown to maroon, pale green
Line color not defined
transparency transparent to translucent
shine glare-like, metallic sheen
Crystal optics
Refractive index n  = 2.137
Birefringence none, as it is optically isotropic

Oldhamite (pronounced: [əʊldə'mɪt;]) is a seldom occurring mineral from the mineral class of "sulfides and sulfosalts" with the idealized chemical composition CaS and is therefore chemically calcium sulfide . Since a small proportion of calcium can occasionally be replaced ( substituted ) by magnesium , the formula is also given with (Ca, Mg) S in some sources.

Oldhamite crystallizes in the cubic crystal system , but rarely develops visible crystal forms that can be up to three millimeters in size. So far, the mineral was found almost exclusively in meteorites , where it appeared in the form of granular to massive mineral aggregates and fine veins . Oldhamite is clear to translucent and is light brown to maroon in color. Fresh samples have a glare-like , metallic sheen , but the surfaces tarnish quickly in moist air.

With a Mohs hardness of 4, Oldhamite is one of the medium-hard minerals and, like the reference mineral fluorite, can be easily scratched with a pocket knife .

Etymology and history

Thomas Oldham, 1895

Oldhamite was first discovered in the Bustee meteorite , which fell in the Basti district of the Indian state of Uttar Pradesh . The mineral was first described in 1862 by Nevil Story Maskelyne (1823-1911), who named it after the Irish geologist Thomas Oldham (1816-1878).

Type material of the mineral is kept in the Natural History Museum of London in England (catalog no. 32100).

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the oldhamite belonged to the mineral class of "sulfides and sulfosalts" and there to the department of "sulfides with the molar ratio of metal: S, Se, Te ≈ 1: 1", where together with Alabandin , Altait , Clausthalit , Crerarit , Galenit , Keilit and Niningerit, he created the "Galenit series" with the system no. II / C.15 formed.

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 classifies oldhamite in the category of "Metal sulfides, M: S = 1: 1 (and similar)". However, this is further subdivided according to the predominant metals in the compound, so that the mineral according to its composition can be found in the sub-section "with tin (Sn), lead (Pb), mercury (Hg) etc.", where it can be found together with Alabandin, Altait, Clausthalit, Galenit, Keilit and Niningerit the "Galenitgruppe" with the system no. 2.CD.10 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns oldhamite to the class of "sulphides and sulphosalts" and there into the category of "sulphide minerals". Here it is also in the " Galena group (isometric: Fm3m) " with the system no. 02.08.01 within the subsection "Sulphides - including selenides and tellurides - with the composition A m B n X p , with (m + n): p = 1: 1".

Crystal structure

Oldhamite crystallizes cubically in the space group Fm 3 m (space group no. 225) with the lattice parameter a  = 5.69  Å and four formula units per unit cell . Template: room group / 225

Education and Locations

Oldhamite forms due to its high melting point of 2450 ° C as an early condensate into cosmic mists , where he may be in the interstices of the subsequently formed enstatite - chondrites - and achondrite settles. Besides enstatite can be used as accompanying minerals under a different pyroxene , calcite , gypsum , niningerite , osbornite and Troilite occur.

As a rare mineral formation, Oldhamite could only be detected at a few sites, whereby so far (as of 2014) around 40 sites are known. Its type locality , the Bustee meteorite, is the only known site in India to date.

In Germany oldhamite was found in the second fragment of the Neuschwanstein meteorite , but also in the Absetzerhalde Lichtenberg of uranium - deposit Ronneburg .

The mineral is also known from various stone and iron meteorites found in Antarctica, Azerbaijan, China, Estonia, Finland, France, Yemen, Canada, Malawi, Morocco, New Zealand, Nigeria, Pakistan, Poland, Russia, the Sahara , South Africa, Sudan, and the United States of America (USA).

Oldhamite can, however, also be anthropogenic in some smelting processes .

See also

literature

Web links

Commons : Oldhamite  - 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.  90 .
  2. ↑ a b c d e f g Oldhamite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001 ( handbookofmineralogy.org PDF; 58.9 kB)
  3. ↑ Mindat - Number of localities for Oldhamit
  4. ↑ location list for the oldhamite Mineralienatlas and Mindat
  5. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  439 (first edition: 1891).