Tephroit
| Tephroit | |
|---|---|
 |
|
| General and classification | |
| chemical formula | Mn 2 SiO 4 |
|
Mineral class (and possibly department) |
Silicates and Germanates |
|
System no. to Strunz and to Dana |
9.AC.05 ( 8th edition : VIII / A.03) 51.03.01.04 |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-dipyramidal; 2 / m 2 / m 2 / m |
| Space group | Pbnm (No. 62, position 3) |
| Lattice parameters | a = 4.90 Å ; b = 10.60 Å; c = 6.26 Å |
| Formula units | Z = 4 |
| Twinning | after {011} |
| Physical Properties | |
| Mohs hardness | 6th |
| Density (g / cm 3 ) | measured: 3.87 to 4.12; calculated: 4.15 |
| Cleavage | imperfect after {001}, clearly after {010} |
| Break ; Tenacity | uneven to shell-like; brittle |
| colour | meat-red, gray-green, reddish-brown |
| Line color | gray-white |
| transparency | transparent to translucent |
| shine | Glass gloss to fat gloss, matt |
| Crystal optics | |
| Refractive indices |
n α = 1.759 n β = 1.797 n γ = 1.860 |
| Birefringence | δ = 0.101 |
| Optical character | biaxial negative |
| Axis angle | 2V = 60 to 70 ° |
Tephroit , also called manganese peridot , is a rarely occurring mineral from the mineral class of " silicates and germanates ". It crystallizes in the orthorhombic crystal system with the chemical composition Mn 2 SiO 4 and develops mostly short prismatic crystals in the centimeter range, but also granular to massive aggregates .
The pure Mn (Tephroit), Mg ( Forsterite ) and Fe compounds ( Fayalite ) can be mixed without gaps , the links between which are known as olivines .
Etymology and history
The forsterite was first found in 1823 in the Sterling Hill Mine near Ogdensburg in Sussex County (New Jersey) and described by August Breithaupt . He named the mineral because of its often ash-gray color after the Greek word "tephra" for ash .
classification
In the old (8th edition) and new systematics of minerals according to Strunz (9th edition) , the Tephroit belongs to the division of " island silicates (nesosilicates)" and there to the oliving group , formed from the minerals fayalite, forsterite, laihunite , Liebenbergite and tephroit .
The revised 9th edition of Strunz's mineral systematics divides this department more precisely according to the possible presence of further anions and the coordination of the cations involved . The Tephroit is accordingly in the sub-section of "Island silicates without additional anions; Cations in octahedral [6] he coordination ”and is still a member of the olive group there, which, however, has been expanded to include the minerals glaucochroit and cherry stone .
The systematics of minerals according to Dana , which is common in the English-speaking world , assigns the Tephroit to the division of " Island silicates: SiO 4 groups with all cations only in octahedral [6] coordination ", similar to the new Strunz'sche mineral systematics . The Oliving group, which can also be found there, consists of the members Fayalit, Forsterit, Laihunit, Liebenbergit and Tephroit, as in the old Strunzian system, but expanded to include olivine, for which the IMA / CNMNC is still lacking recognition.
Crystal structure
Tephroit crystallizes orthorhombically in the space group Pbnm (space group no. 62, position 3) with the lattice parameters a = 4.90 Å ; b = 10.60 Å and c = 6.26 Å as well as four formula units per unit cell .
properties
Tephroit gets its reddish-brown to flesh-red color from its manganese content . In nature, however, Tephroit is often found in the form of mixed crystals with fluctuating contents of forsterite and / or fayalite. The color varies accordingly towards gray or olive green.
Modifications and varieties
As Roepperit one is zinc-containing variety of Tephroit or fayalite (after Brush), respectively.
Education and Locations
Tephroite forms in iron - manganese deposits , related skarns, and metamorphic , manganese - rich sediments . Accompanying minerals include alleghanyite , banalsite , bustamite , calcite , diopside , franklinite , gageit , glaucochroit , jacobsite , manganocalcite , rhodonite , willemite and zincite .
Tephroit has so far been detected at around 180 sites worldwide (as of 2010), for example in the Antarctic , Australia , Brazil , China , Germany , Finland , France , India , Italy , Japan , Kazakhstan , Kyrgyzstan , Madagascar , Namibia , Norway , Oman , Austria , Russia , Sweden , Switzerland Slovakia , Spain , South Africa , Czech Republic , Turkey , United Arab Emirates , United Kingdom (Great Britain) and United States (USA).
Use as a gem stone
The minerals of the Oliving group are mainly processed into gemstones if they are of good quality . Clear varieties usually have a facet cut in different shapes, while cloudy varieties tend to have a cabochon cut. They are commercially available under the name "Peridot" or "Chrysolite".
See also
literature
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 195 .
Web links
- Mineral Atlas: Tephroit (Wiki)
Individual evidence
- ^ David Barthelmy: Tephroite Mineral Data. In: webmineral.com. Retrieved September 14, 2019 .
- ^ 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. 538 (English).
- ↑ a b Tephroite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 77 kB ; accessed on September 14, 2019]).
- ↑ a b c d e Tephroite. In: mindat.org. Hudson Institute of Mineralogy, accessed September 14, 2019 .
- ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
- ↑ Roepperite (of Brush). In: mindat.org. Hudson Institute of Mineralogy, accessed September 14, 2019 .
- ↑ Find location list for Tephroit at the Mineralienatlas and at Mindat
- ^ Walter Schumann: Precious stones and gemstones. All kinds and varieties. 1900 unique pieces . 16th, revised edition. BLV Verlag, Munich 2014, ISBN 978-3-8354-1171-5 , pp. 174 .