Omphacit
| Omphacit | |
|---|---|
 |
|
| General and classification | |
| other names |
Omphazit |
| chemical formula | (Ca, Na) (Mg, Fe, Al) Si 2 O 6 |
|
Mineral class (and possibly department) |
Silicates and Germanates |
|
System no. to Strunz and to Dana |
9.DA.20 ( 8th edition : VIII / F.01) 65.01.03b.01 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Space group | C 2 / c (No. 15) or P 2 / n (No. 13, position 2) |
| Lattice parameters |
a = 9.59 Å ; b = 8.78 Å; c = 5.26 Å β = 106.8 ° |
| Formula units | Z = 4 |
| Twinning | often single and polysynthetic twins on {100} |
| Physical Properties | |
| Mohs hardness | 5 to 6 |
| Density (g / cm 3 ) | 3.16 to 3.43 (measured); 3.36 (calculated) |
| Cleavage | well after {110}, (110) or (110) ~ 87 ° |
| Break ; Tenacity | uneven to shell-like; brittle |
| colour | grass green, emerald green, dark green |
| Line color | greenish white |
| transparency | translucent |
| shine | Glass gloss or silk gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.662 to 1.701 n β = 1.670 to 1.712 n γ = 1.685 to 1.723 |
| Birefringence | δ = 0.023 |
| Optical character | biaxial positive |
| Axis angle | 2V = 58 to 83 ° (measured); 74 to 88 ° (calculated) |
| Pleochroism | weak: X = colorless, Y = very light green, Z = very light green to bluish green |
| Other properties | |
| Special features | high relief and poorly soluble in hydrochloric acid |
The mineral omphacite outdated, even omphacite written, is a rarely occurring chain silicate from the group of pyroxene within the mineral class of "silicates and Germanates". It crystallizes in the monoclinic crystal system with the chemical composition (Ca, Na) (Mg, Fe, Al) [Si 2 O 6 ]. The elements calcium and sodium or magnesium , iron and aluminum indicated in the round brackets can represent each other in the formula ( substitution , diadochie), but are always in the same proportion to the other components of the mineral.
Omphacit rarely develops coarse crystals up to about five centimeters in size and a glass-like sheen on the surfaces. It usually occurs in the form of irregular, xenomorphic grains or massive mineral aggregates . In its pure form, Omphacite is grass-green or emerald-green to dark green in color and has a greenish-white streak color . It is a main component of the eclogite metabasite .
Etymology and history
The mineral was first discovered in a former quarry near Silver Creek in the municipality Konradsreuth in the Bavarian region of Upper Franconia and described in 1815 by Abraham Gottlob Werner , of the mineral based on its color after the ancient Greek word ὄμφαξ [omphax] for unripe grape called omphacite . However, this spelling was corrected in later mineralogical publications on Omphacit and became generally accepted.
Type material of the mineral is kept in the mineralogical collection of the Technical University Bergakademie Freiberg (catalog no. 100568 / K 103).
classification
In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the Omphacit belonged to the department of " chain and band silicates (inosilicates) ", where it together with aegirine , augite , diopside , esseneit , hedenbergite , jadeite , jervisite , johannsenite , kanoite , clino , Klinoferrosilit , Kosmochlor , Namansilit , Natalyit , Petedunnit , pigeonite and spodumene the "pyroxene, clinopyroxene subgroup" with the system no. VIII / F.01 within the pyroxene group .
The 9th edition of Strunz's mineral systematics, which has been in force since 2001 and is used by the International Mineralogical Association (IMA), also classifies Omphacit in the category of “chain and band silicates (inosilicates)”. However, this department is further subdivided according to the type of chain formation, so that the mineral is classified in the subdivision “Chain and band silicates with 2-periodic single chains Si2O6; Pyroxen family "can be found, where together with the aegirin-augite and chromomphacite the" Ca-Na-clinopyroxene, omphacite group "with the system no. 9.DA.20 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Omphacit to the class of "silicates and Germanates" and there in the department of "chain silicate minerals". Here it is together with the Aegirin-Augit in the group of " C 2 / c clinopyroxenes (intermediate clinopyroxenes)" with the system no. 65.01.03b can be found in the subsection " Chain Silicates: Simple unbranched chains, W = 1 with chains P = 2 ".
Crystal structure
Omphacite crystallizes monoclinically in the space group C 2 / c (space group no. 15) or P 2 / n (no. 13, position 2) with the lattice parameters a = 9.59 Å ; b = 8.78 Å; c = 5.26 Å; β = 106.8 ° and four formula units per unit cell .
Education and Locations
Omphacite forms in basic to ultra-basic, metamorphic rocks such as the metabasite eclogite , of which it is one of the main components. This occurs at high pressures from approx. 10 kbar (corresponds to approx. 35 km depth) and medium to high temperatures (500 to 1000 degrees Celsius). Omphacite is also found frequently in kimberlites and granulites , but also in some ophiolites and blue schist facies containing glaucoma .
As a rather rare mineral formation, omphacite can sometimes be abundant at various sites, but overall it is not very common. So far (as of 2014) around 190 sites are known. As Begleitminerale enter into eclogites among other garnet , corundum , kyanite and quartz , however, in blueschists rather epidote , glaucophane , hornblende and scapolite on.
In Germany, Omphacit could be found in addition to its type locality Silberbach in several places in the Münchberger Gneismasse in Bavaria, in the Clara pit near Oberwolfach in Baden-Württemberg, in the Nickenich vineyard in Rhineland-Palatinate and in several places in the Saxon Ore Mountains .
In Austria, the mineral was found on the Hüttenberger Erzberg and at various sites in the Koralpe and Saualpe in Carinthia, near Gansbach (community of Dunkelsteinerwald) and near Altenburg in Lower Austria, near Krumbach (community of Eibiswald ) and Wernersdorf in Styria and in the Sulztal ( Stubai Alps) in Tyrol.
In Switzerland, Omphacit has so far only appeared on the Alpe Arami near the municipality of Gorduno in the canton of Ticino and on the Allalinhorn ( Allalin for short ) in the municipality of Saas-Almagell in the canton of Valais.
Other locations are in Afghanistan, Australia, Brazil, China, France, Greece, Guatemala, India, Italy, Japan, Lesotho, Canada, Columbia, Cuba, Mexico, New Caledonia, Nigeria, Norway, Pakistan, Poland, Russia, Slovenia, South Africa, the Czech Republic, Turkey, the United Kingdom (UK), the United States of America (USA) and Venezuela.
See also
literature
- Abraham Gottlob Werner : Abraham Gottlob Werner's last mineral system. Issued from his estate by order of the Mining Authority and provided with explanations. Freiberg and Vienna 1817. p. 33 ( available online in the Google book search)
- Helmut Schrätze, Karl-Ludwig Weiner: Mineralogy. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 772 .
- Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p. 526 .
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 234 ( Dörfler Natur ).
Web links
- Mineral Atlas: Omphacit (Wiki)
- Webmineral - Omphacite
- Database-of-Raman-spectroscopy - Omphacite
- American-Mineralogist-Crystal-Structure-Database - Omphacite
Individual evidence
- ↑ a b c Omphacit. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001 ( PDF kB ).
- ↑ a b Mindat - Omphacit
- ^ A b c Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 620 .
- ^ IMA / CNMNC List of Mineral Names; March 2014 (PDF 1.5 MB)
- ↑ a b Type mineral catalog of the University of Hamburg
- ↑ Mindat - Number of localities for Omphacit
- ↑ Find location list for Omphacit in the Mineralienatlas and Mindat