Calvertite

Calvertite
General and classification
other names	IMA 2006-030
chemical formula	Cu 5 Ge 0.5 S 4
Mineral class; (and possibly department)	Sulfides and sulfosalts
System no. to Strunz ; and to Dana	2.CA.15 ( 8th edition : II / B.02) ; 05/02/10/02
Crystallographic Data
Crystal system	cubic
Crystal class ; symbol	cubic hexakisoctahedral; 4 / m 3 2 / m , cubic hexakistrahedral; 4 3 m ; or pentagon-icositetrahedral; 432
Space group	Fm 3 m (No. 225) , F 4 3 m (No. 216) or F 432 (No. 209)
Lattice parameters	a = 5.337 Å
Formula units	Z = 1
Physical Properties
Mohs hardness	4 to 5, VHN 25 = 283 (268-307) kg / mm 2
Density (g / cm 3 )	5.239 (calculated)
Cleavage	no
Break ; Tenacity	uneven to shell-like; brittle
colour	black
Line color	black
transparency	opaque
shine	Metallic luster
Crystal optics
Optical character	optically isotropic

Calvertite is a very rarely occurring mineral from the mineral class of " sulfides and sulfosalts ". It crystallizes in the cubic crystal system with the chemical composition Cu ₅ Ge _0.5 S ₄ and is therefore chemically a copper - germanium - sulfide .

Calvertite develops xenomorphic , elongated to ellipsoidal grains up to 0.1 mm in size, which sit in an ore matrix of renierite in which tennantite and inclusions of gallite occur locally .

Etymology and history

During the investigation of the holotype specimen of gallobeudantite , which was probably recovered from the Tsumeb Mine around 1960, partially oxidized, copper-rich massive sulphides were identified in its ore matrix. In addition to renierite with inclusions of gallite , gallium-containing tennantite and chalcosine , a sulphidic ore mineral was also encountered, which in the X-ray diffraction analysis showed a germanite-like diffractogram , but was too copper-rich for germanite and initially remained unidentified. Upon further investigation, this sulfide turned out to be a new mineral. It was recognized by the International Mineralogical Association (IMA) in 2006 and by a US-Canadian-English research team including John Leslie Jambor , Andrew C. Roberts , Lee A. Groat , Chris J. Stanley , Alan J. Criddle and Mark in 2007 N. Described finely as calvertite. The mineral was named after the metallurgist Lauriston (Larry) Derwent Calvert (1924-1993) of the National Research Council of Canada , Ottawa , Canada , for his studies of metallic phases and contributions to the Powder Diffraction File (ICDD).

Type material of the mineral is kept in the Canadian Museum of Nature in Ottawa (Cotype, Polished Grind, Collection No. CMNMC 85731) and in the Natural History Museum , London , United Kingdom (Cotype, Polished Grind, Collection No. BM 2004, 78) .

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the calvertite belonged to the department of "Sulphides, Selenides and Tellurides with a ratio of metal: S, Se, Te> 1: 1", where it together with Bornite , Betechtinit and Gortdrumit the group of the "complex copper-iron-sulfides" with the system no. II / B.02 .

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 calvertite 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 can be found according to its composition in the sub-section "with copper (Cu)", where it is the only member of the unnamed group 2.CA.15 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the calvertite to the class of "sulfides and sulfosalts" and there in the department of "sulfide minerals". Here it can be found together with Putzit in the unnamed group 02.05.10 within the subsection “Sulphides - including selenides and tellurides - with the composition A _m B _n X _p , with (m + n): p = 3: 2”.

Chemism

Calvertite has the measured chemical composition (Cu, Fe, Zn, Ga, V) _Σ5.00 (Ge, As) _Σ0.48 S ₄ , which was idealized to Cu ₅ Ge _0.5 S ₄ and contents of 65.88% Requires Cu, 7.53% Ge, and 26.59% S. In chemical terms, calvertite does not resemble any other natural or synthetic Cu or Cu-Ge sulphide. The small unit cell suggests that calvertite is a metastable, highly disordered mineral, the ordered equivalent of which can be chemically described as Cu ₁₀ GeS ₈ with a = 2 × 5.337 Å = 10.674 Å and Z = 4.

Crystal structure

Calvertite crystallizes in the cubic crystal system in space group Fm 3 m (space group no.225) , space group F 4 3 m (space group no.216 ) or space group F 432 (space group no.209 ) with the lattice parameters a = 6.631 Å and one formula unit per unit cell . Template: room group / 225 Template: room group / 216 Template: room group / 209

Only four measurable lines can be identified in the X-ray diffraction pattern of the calvertite. The X-ray diffraction pattern of calvertite is similar to that of the synthetic component Cu ₃ GeS ₄ , but also to those of renierite (tetragonal), germanocolusite (cubic) and germanite (cubic).

A crystal structure model for the calvertite does not yet exist (as of 2016).

properties

morphology

In calvertite-rich parts of the type stage, chalcosine forms a network with a granular texture in which the calvertite occurs xenomorphically and mostly in the form of elongated to elliptical grains. The largest homogeneous grains reach a diameter of 100 µm. The main sulphides of the stage, renierite and calvertite, are concentrated in band-like accumulations; such calvertitic bands penetrate locally renierite and inclusions of tennantite in renierite.

physical and chemical properties

The aggregates of the calvertite are black, and the line color is also described as black. The surfaces of the opaque grains show a metallic luster .

The mineral has no cleavage or divisibility, but because of its brittleness it breaks like glass or quartz , with the fracture surfaces being uneven to shell-shaped. With a Mohs hardness of 4 to 5, calvertite is one of the medium-hard minerals that are somewhat easier to scratch with a pocket knife than the reference mineral apatite . The calculated density is 5.239 g / cm³. Calvertit does not fluoresce in the long or short wave UV range.

In the reflected light (bevel), Calvertite is pale bluish-gray and shows neither bireflectance nor pleochroism and also no internal reflexes . The optical properties of calvertite are neither similar to those of germanite nor those of any other ore mineral.

Education and Locations

As a very rare mineral formation, calvertite could so far (as of 2016) only be described by its type locality . This is the world-famous Cu-Pb-Zn-Ag-Ge-Cd deposit of the "Tsumeb Mine" (Tsumcorp Mine) in Tsumeb , Oshikoto region , Namibia . It was found in primary ore paragenesis together with renierite, tennantite, gallite, chalcosine and another unidentified copper sulfide (or a mixture of digenite and djurleit ). Calvertite was later formed as renierite, as it pervades the older renierite in the form of small passages. Goethite , hematite , quartz , mercury- rich solid silver , stolzite , otjisumeit and various representatives of the alunite supergroup, including gallobeudantite , were identified among the associated non- ore minerals of the type level .

use

Due to its rarity, calvertite is only of interest to mineral collectors.

literature

John Leslie Jambor , Andrew C. Roberts, Lee A. Groat, Chris J. Stanley, Alan J. Criddle, Mark N. Feinglos (2000): Calvertite, Cu ₅ Ge _0.5 S ₄ , a new mineral species from Tsumeb, Namibia. In: The Canadian Mineralogist , Volume 45, pp. 1519-1523, doi : 10.3749 / canmin.45.6.1519 .
Paula C. Piilonen, Glenn Poirier, Kimberly T. Tait (2008): New Mineral Names. In: American Mineralogist , Volume 93, p. 1686 ( PDF, 860 kB ).
Calvertit , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America, 2013 ( PDF, 81 kB ).

Web links

Individual evidence

↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u John Leslie Jambor , Andrew C. Roberts, Lee A. Groat, Chris J. Stanley, Alan J. Criddle, Mark N. Feinglos (2000): Calvertite, Cu ₅ Ge _0.5 S ₄ , a new mineral species from Tsumeb, Namibia. In: The Canadian Mineralogist , Volume 45, pp. 1519-1523.
↑ Mindat - Number of localities for Calvertite
↑ List of localities for calvertite in the Mineralienatlas and Mindat

[Jambor-1] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u John Leslie Jambor , Andrew C. Roberts, Lee A. Groat, Chris J. Stanley, Alan J. Criddle, Mark N. Feinglos (2000): Calvertite, Cu ₅ Ge _0.5 S ₄ , a new mineral species from Tsumeb, Namibia. In: The Canadian Mineralogist , Volume 45, pp. 1519-1523.

[MindatAnzahl-2] Mindat - Number of localities for Calvertite

[Fundorte-3] List of localities for calvertite in the Mineralienatlas and Mindat