Cassiterite
| Cassiterite | |
|---|---|
 |
|
| General and classification | |
| other names |
|
| chemical formula | SnO 2 |
|
Mineral class (and possibly department) |
Oxides, hydroxides - molar ratio metal: oxygen = 1: 2 |
|
System no. to Strunz and to Dana |
4.DB.05 ( 8th edition : IV / D.02) 04.04.01.05 |
| Crystallographic Data | |
| Crystal system | tetragonal |
| Crystal class ; symbol | ditetragonal-dipyramidal; 4 / m 2 / m 2 / m |
| Space group | P 4 2 / mnm (No. 136) |
| Lattice parameters | a = 4.74 Å ; c = 3.19 Å |
| Formula units | Z = 2 |
| Frequent crystal faces | {111}, {110}, {100}, {321} |
| Twinning | often, also Viellinge |
| Physical Properties | |
| Mohs hardness | 6 to 7 |
| Density (g / cm 3 ) | 6.3 to 7.2 |
| Cleavage | completely after {100}, indistinct after {110} |
| Break ; Tenacity | shell-like, brittle |
| colour | brown-black, gray, yellow-brown, green, red |
| Line color | yellow-white to colorless |
| transparency | translucent to opaque |
| shine | Diamond luster, fat luster |
| Crystal optics | |
| Refractive indices |
n ω = 2.000 to 2.006 n ε = 2.097 to 2.100 |
| Birefringence | δ = 0.097 |
| Optical character | uniaxial positive |
| Pleochroism | weak dichroism, yellow-red-brown |
Cassiterite , outdated also known as pewter stone , needle pewter (ore) , wood pewter , barley and cassiterite , is a common mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the tetragonal crystal system with the chemical composition SnO 2 , so from a chemical point of view it is tin (IV) oxide and the most economically important ore for the extraction of tin .
Cassiterite usually develops short to long, prismatic, needle-shaped or bipyramidal crystals , but also granular to massive aggregates in brown-black, gray, yellow-brown, green or red color. Colorless crystals are also known. Translucent crystals show weak dichroism in yellow and reddish brown.
Etymology and history
The name cassiterite is derived from the Greek κασσίτερος kassiteros for tin . Miners referred to the short-prismatic and knee- shaped angled crystal twins or many-quarters as visor barbs . Aggregates in a nieriger, glass-headed formation were given the designation wood tin .
The mineral has been used since the 6th millennium BC due to its high tin content (hence also tin stone ). Mined and belongs to the first ores that were used by humans.
classification
Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , cassiterite belonged to the mineral class of "oxides and hydroxides" and there to the department of "oxides with the molar ratio of metal: oxygen = 1: 2 (MO 2 and related compounds ) ", Where together with argutite , paratellurite , plattnerite , pyrolusite , rutile and tripuhyite the" rutile group "with the system no. IV / D.02 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 cassiterite in the category of "Oxides with the molar ratio of metal: oxygen = 1: 2 and comparable". However, this is further subdivided according to the relative size of the cations involved and the crystal structure, so that the mineral is classified in the sub-section “With medium-sized cations; Chains of edge-linked octahedra "can be found where it forms the" rutile group " 4.DB.05 together with argutite, plattnerite, pyrolusite, rutile, tripuhyite, tugarinovite and varlamoffite .
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns cassiterite to the class of "oxides and hydroxides" and there in the department of "oxides". Here it is together with rutile, ilmenorutile , strüverite, pyrolusite, plattnerite, argutite, squawcreekite and stishovite in the " rutile group (tetragonal: P4 2 / mnm) " with the system no. 04.04.01 to be found in the subsection “Simple oxides with a cation charge of 4+ (AO 2 )”.
Crystal structure
Cassiterite crystallizes in the tetragonal crystal system in the space group P 4 2 / mnm (space group no. 136) with the lattice parameters a = 4.74 Å , c = 3.19 Å and two formula units per unit cell .
Education and Locations
Cassiterite occurs mainly in hydrothermal veins , greisen and granitic pegmatites . It is also found as soapy tin in river sediments.
Cassiterite is found in paragenesis with many different minerals, including quartz , muscovite , various tourmalines , topaz , fluorite , lepidolite , scheelite and ore minerals such as " wolframite ", arsenopyrite , molybdenite and tantalite (Mn) .
The deposits in the Ore Mountains, Fichtel Mountains and Cornwall were historically significant . The most important deposits with current mining are in Llallagua and Viloco in Bolivia , Hunan and Yunnan in the People's Republic of China , Indonesia , Malaysia and Peru .
Other sites were or are, among others, some regions in Afghanistan ; the provinces of Constantine and Tamanrasset in Algeria ; the provinces of Jujuy , Salta , San Juan and San Luis in Argentina ; Rossard / Tasmania and many other regions in Australia ; Liege in Belgium ; Belize ; many regions in Bolivia ; Amazonas , Bahia , Goiás and Minas Gerais in Brazil ; many regions in the People's Republic of China; some regions in France ; many regions in the UK ; some regions in Canada ; Katanga , Kivu and Maniema in the Democratic Republic of the Congo ; Hokkaidō , Honshū and Kyūshū in Japan ; Madagascar ; Mexico ; Panasqueira in Portugal , Tenkergin / Chukchi Peninsula in the Russian Federation , Horní Slavkov / Bohemia and Moravia in the Czech Republic ; as well as many regions in the US .
The cassiterite deposits in Eastern Congo are located in a conflict zone, together with coltan , gold and wolframite, cassiterite is one of the main conflict raw materials in this war.
As part of his mineralogical studies, Johann Wolfgang von Goethe also dealt with the cassiterite deposits in Bohemia . He developed his own recovery model for these occurrences. There are several notes in his estate that reveal his interpretation. In the mineralogical textbook Propaedeutics of Mineralogy by Karl Cäsar von Leonhard , a description written by Goethe was printed.
use
As a raw material
With a (theoretical) tin content of 78.8 percent, cassiterite is the only significant tin ore worldwide. However, the tin atoms are often partially replaced by atoms of iron , titanium , niobium , tantalum or zirconium is replaced and thus reduce the actual tin content. Slag from tin smelting is therefore an important raw material for the extraction of tantalum.
For the global output of tin ore see main article tin .
Cassiterite is smelted at temperatures around 1000 degrees Celsius. The pewter obtained is used as a non-toxic, rust-resistant coating on steel containers ( tinplate ), as well as for the production of various household items such as plates or jugs, but also decorative and play objects such as pewter figures . In addition, it is also used as a low-melting soft solder in alloys with lead and other metals .
As a gem
Well-formed crystals are processed into gemstones . However, depending on the tin content, these are very sensitive to various acids and heat. Cassiterite can easily be confused with colored diamonds , smoky quartz , scheelite , zircon and others because of its color and luster .
See also
literature
- Martin Okrusch, Siegfried Matthes: Mineralogy: An introduction to special mineralogy, petrology and deposit science . 7th edition. Springer Verlag, Berlin / Heidelberg / New York 2005, ISBN 3-540-23812-3 .
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 101 .
Web links
Individual evidence
- ↑ Webmineral - cassiterite
- ^ A b c 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. 207 .
- ↑ a b Cassiterite at mindat.org (English)
- ↑ Homepage of Geevor, the last tin mine in Cornwall (English)
- ^ Cassiterite . 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; 71 kB ; accessed on September 14, 2018]).
- ^ Locations for cassiterite at the Mineralienatlas and at Mindat
- ↑ Johannes Baier: Goethe and the Kassiterit von Schlaggenwald (Horní Slavkov; Czech Republic). In: Z. geol. Knowledge 41/42, pp. 267-273; Berlin, 2013/2014 ( summary )