Coquimbit
| Coquimbit | |
|---|---|
 |
|
| General and classification | |
| chemical formula | Fe 2 3+ [SO 4 ] 3 • (6 + 3) H 2 O |
|
Mineral class (and possibly department) |
Sulfates |
|
System no. to Strunz and to Dana |
7.CB.55 ( 8th edition : VI / C.08) 08/29/03/01 |
| Similar minerals | Quenstedtite |
| Crystallographic Data | |
| Crystal system | trigonal |
| Crystal class ; symbol | ditrigonal-scalenohedral; 3 2 / m |
| Space group | P 3 1 c (No. 163) |
| Lattice parameters | a = 10.92 Å ; c = 17.08 Å |
| Formula units | Z = 4 |
| Frequent crystal faces | {1010}, {1120}, {1011}, {0001} |
| Physical Properties | |
| Mohs hardness | 2.5 |
| Density (g / cm 3 ) | measured: 2.11 (1); calculated: [2.12] |
| Cleavage | indistinct |
| Break ; Tenacity | shell-like to uneven |
| colour | colorless, purple, yellow, green, blue |
| Line color | White |
| transparency | transparent |
| shine | Glass gloss |
| Crystal optics | |
| Refractive indices |
n ω = 1.536 to 1.539 n ε = 1.548 to 1.572 |
| Birefringence | δ = 0.012 |
| Optical character | uniaxial positive |
| Other properties | |
| Chemical behavior | water soluble; bitter, metallic taste |
Coquimbit is a rather seldom occurring mineral from the mineral class of " sulfates " with the composition Fe 2 3+ [SO 4 ] 3 · (6 + 3) H 2 O and is therefore chemically a water-containing iron (III) sulfate .
Coquimbit crystallizes in the trigonal crystal system and develops mostly tabular, short prismatic or pyramidal crystals with a glass-like sheen on the surfaces, but also occurs in the form of granular to massive aggregates . Pure coquimbit is colorless and transparent. In nature, however, it usually takes on a pink to purple, rarely yellow, green or blue color due to foreign admixtures. In addition, abnormal interference colors occasionally appear .
With a Mohs hardness of 2.5, coquimbite lies between the reference minerals gypsum (2) and calcite (3) and is therefore still one of the soft minerals that can no longer be scratched with a fingernail, but easily scratched with a copper coin.
Etymology and history
Coquimbit was discovered by Johann Friedrich August Breithaupt in 1841 in a deposit of greenish jasper near Copiapó in the then Chilean province of Coquimbo and named according to its type locality . Type material of the mineral is kept in the Mineralogical Institute of the Technical University Bergakademie Freiberg in Germany (No. 18558).
classification
In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the coquimbit belonged to the mineral class of "sulfates, selenates, tellurates, chromates, molybdates, wolframates" and there to the department of "water-containing sulfates without foreign anions ", where they belong together with Alunogen , Kornelit , Lausenit , meta Alunogen , Paracoquimbit , Quenstedtit and Rhomboklas formed a distinct group.
The 9th edition of Strunz's mineral systematics, valid since 2001 and used by the International Mineralogical Association (IMA), assigns coquimbit to the class of "sulfates (selenates, tellurates, chromates, molybdates and wolframates)" and there in the department of " Sulphates (selenates etc.) without additional anions, with H 2 O “. This section is, however, further subdivided according to the size of the cations involved , so that the mineral can be found according to its composition in the sub-section “With only medium-sized cations”, where the “rhomboclase group” with system no. 7.CB.55 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the coquimbit to the class of "sulfates, chromates and molybdates" and there to the category of "water-containing acids and sulfates". Here he is to be found as the only member of the unnamed group 08/29/03 within the subdivision of " Hydrous acids and sulfates with (A) 2 (XO 4 ) 3 × x (H 2 O) ".
Crystal structure
Coquimbit crystallizes trigonal in the space group P 3 1 c (space group no.163) with the lattice parameters a = 10.92 Å and c = 17.08 Å as well as 4 formula units per unit cell .
Paracoquimbit , a modification of Coquimbit, has a different space group with the same chemical composition, the same crystal system and similar properties, namely R 3 (No. 148) (trigonal-rhombohedral) with the lattice parameters a = 10.93 Å and c = 51, 3 Å and 12 formula units per unit cell.
properties
Since the mineral is already soluble in cold water, it must be stored away from moisture.
Education and Locations
Coquimbit forms as a typical secondary mineral mainly by oxidation in iron sulfide - deposits (mostly of pyrite ), but can also be called by sublimation from volcanic vapors or burning heaps arise. It occurs in paragenesis with various other sulfate minerals such as Copiapit , Paracoquimbit , Voltait , Szomolnokit and Römerit on.
As a rather rare mineral formation, coquimbite can sometimes be found in abundance at different locations, but overall it is not very common. So far (as of 2016) around 130 sites are known. In addition to its type locality Copiapó in the Coquimbo region, the mineral occurred in Chile in several mines on Mejillones , in Caracoles and Calama in the Región de Antofagasta and Tierra Amarilla near Copiapó in the Región de Atacama.
In Germany, Coquimbit has so far been found in the Clara mine near Oberwolfach in Baden-Württemberg, on Rammelsberg near Goslar in Lower Saxony, in the Julia colliery near Herne in North Rhine-Westphalia and on the now closed waste dump of the Lichtenberg opencast mine near Ronneburg in Thuringia.
In Austria, the mineral has so far only been found in the Galgenberg railway tunnel near Leoben and in the Spitzmühle quarry near Leutschach in Styria, and in Switzerland Coquimbit has only occurred at Brissago TI in the canton of Ticino and on Mont Chemin near Martigny in the canton of Valais.
Other locations include Argentina, Australia, Belgium, Bolivia, China, Mongolia, France, Greece, Iran, Italy, Japan, Morocco, Peru, Portugal, Russia, Slovakia, South Africa, Spain, the Czech Republic, Hungary, the United States States of America (USA) and Cyprus.
See also
literature
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Dörfler Verlag GmbH, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 144 .
Web links
- Mineral Atlas: Coquimbit (Wiki)
Individual evidence
- ↑ 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. 385 .
- ↑ Webmineral - Coquimbite (English)
- ↑ a b c d Coquimbite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 64.5 kB )
- ↑ a b c Mindat - Coquimbite
- ↑ Catalog of Type Mineral Specimens - C. (PDF 131 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed August 29, 2019 .
- ↑ Webmineral - Paracoquimbite (English)
- ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 608 (first edition: 1891).
- ↑ Mindat - Number of localities for Coquimbit
- ↑ Find location list for Coquimbit at the Mineralienatlas and at Mindat