Forsterite
| Forsterite | |
|---|---|
 with hematite (reddish crystals) |
|
| General and classification | |
| chemical formula | Mg 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.04) 03/01/01/02 |
| 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 = 4.80 Å ; b = 10.35 Å; c = 6.06 Å |
| Formula units | Z = 4 |
| Physical Properties | |
| Mohs hardness | 7th |
| Density (g / cm 3 ) | 3.275 |
| Cleavage | good after {001}, clearly after {010} |
| Break ; Tenacity | shell-like to uneven |
| colour | colorless, gray-white, green, yellow, yellow-green to black-green |
| Line color | White |
| transparency | transparent to translucent |
| shine | Glass gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.636 to 1.730 n β = 1.650 to 1.739 n γ = 1.669 to 1.772 |
| Birefringence | δ = 0.033 to 0.042 |
| Optical character | biaxial positive |
| Axis angle | 2V = 74 to 90 ° |
Forsterite is a common mineral from the mineral class of " silicates and germanates ". It crystallizes in the orthorhombic crystal system with the chemical composition Mg 2 [SiO 4 ] and develops mostly tabular to prismatic crystals , but also granular aggregates .
Forsterite forms a seamless mixed series with fayalite and tephroit , the links of which are called olivine .
Etymology and history
The forsterite was first found in 1824 on Monte Somma in Italy and described by Armand Lévy , who named the mineral after Adolarius Jacob Forster (1739–1806), an English mineral collector and dealer.
classification
In the old (8th edition) and new systematics of minerals according to Strunz (9th edition) , forsterite belongs to the division of " island silicates (nesosilicates)" and there to the oliving group , formed from the minerals fayalite, forsterite, laihunite , love mountainite and tephroit .
The revised 9th edition of Strunz's mineral systematics divides this department more precisely according to the presence or absence of further anions and the coordination of the cations involved . The forsterite is accordingly in the sub-section of “Island silicates without further anions; with cations in octahedral [6] 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 forsterite 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
Forsterite crystallizes orthorhombically in the space group Pbnm (space group no. 62, position 3) with the lattice parameters a = 4.80 Å determined in several measurements from 2007 ; b = 10.35 Å and c = 6.06 Å as well as four formula units per unit cell .
properties
Pure forsterite is colorless or gray-white due to lattice defects or impurities. In nature, however, forsterite is rarely found in its pure form, but almost always with fluctuating fayalite and / or tephroite content. Are color factor ie in fayalite (brown to black) vast iron - ions or the (gray, red) in Tephroit predominant manganese ions, the forsterite with an increasing percentage of its light green to yellow green and brown green give to black green.
Modifications and varieties
The compound Mg 2 [SiO 4 ] is trimorph , so come next to the orthorhombic forsterite even as also orthorhombic, albeit with a different space group and other cell parameters, crystallizing ringwoodite (γ- (Mg, Fe) 2 [SiO 4 ]) and as cubic crystallizing wadsleyite (β- (Mg, Fe) 2 [SiO 4 ]).
At high pressure, forsterite converts by phase transformation in the high pressure - modification Wadsleyit order. Under the conditions prevailing in the Earth's upper mantle, this transition occurs at around 14 to 15 GPa. In high-pressure experiments, however, the phase transition can take place with a delay, so that forsterite can remain metastable up to almost 50 GPa at room temperature (see figure).
Education and Locations
Forsterite forms in mafic to ultramafic volcanic rocks and in metamorphic converted dolomitic limestones . There it occurs in paragenesis with a whole range of minerals such as calcite , chromite , dolomite , enstatite , corundum , magnetite , phlogopite , plagioclase and spinel .
So far, forsterite has been found at more than 960 sites (as of 2014). In addition to its type locality Monte Somma, forsterite was found in Italy in the Vulture area , as well as in Apulia , Latium , Liguria , Lombardy , Piedmont , Sicily , Trentino-South Tyrol , Tuscany and Umbria .
Other locations are Egypt , Algeria , Angola , Antarctica , Ethiopia , Australia , Bolivia , Botswana , Brazil , Bulgaria , China , Germany , Finland , France , Greece , Greenland , India , Indonesia , Iraq , Japan , Kazakhstan , Canada , Colombia , Madagascar , Mexico , Myanmar , Namibia , New Caledonia , New Zealand , North Korea , Norway , Austria , Poland , Russia , Scotland (Great Britain), Sweden , Switzerland , Slovakia , Spain , South Africa , Tajikistan , Tanzania , Czech Republic , Turkey , Hungary , Ukraine and the USA .
In April 2011, an American research team reported the discovery of forsterite crystals in the protostellar cloud of the protostar HOPS-68 with the help of the Spitzer Space Telescope . The scientists assume that the initially amorphous material is tempered near the protostar and crystallizes in the process, before it is transported to the cooler outer area of the dust envelope by transport processes. Forsterite has also been detected by infrared spectroscopy in other cosmic environments - for example in several comets (including Comet Halley , Comet Hale-Bopp ), in the dust envelopes of pulsating red giants, in planetary nebulas and in protoplanetary disks (i.e. planetary systems that are emerging).
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".
Due to the color, there is a risk of confusion with beryl , chrysoberyl , demantoid , diopside , prasiolite , prehnite , sinhalite , emerald , tourmaline and vesuvianite .
Manipulations and imitations
In order to enhance stones with a weak color, they are occasionally placed under a green foil in ring or pendant settings. Also imitations of colored glass or synthetic corundum or spinel issued by rogue vendors as peridot. In contrast to these, forsterite or its mixed crystals can be recognized by the strong birefringence, which can be recognized when looking through thicker, faceted stones from the doubling of the lower facet edges, even without a magnifying glass.
See also
literature
- Petr Korbel, Milan Novák: Mineral Encyclopedia (= Villager Nature ). Edition Dörfler im Nebel-Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 194 .
- Forsterite . 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; 76 kB ; accessed on June 10, 2019]).
Web links
- Mineral Atlas: Forsterite (Wiki)
- Michael RW Peters: Peridot. In: www.realgems.org. RealGems, November 30, 2016, accessed June 10, 2019 (with image examples of cut stones).
Individual evidence
- ^ A b c David Barthelmy: Forsterite Mineral Data. In: webmineral.com. Retrieved June 10, 2019 .
- ↑ a b c American-Mineralogist-Crystal-Structure-Database - Forsterite. In: rruff.geo.arizona.edu. Retrieved June 10, 2019 .
- ↑ a b Forsterite . 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; 76 kB ; accessed on June 10, 2019]).
- ↑ a b c d e Forsterite. In: mindat.org. Hudson Institute of Mineralogy, accessed June 10, 2019 .
- ^ A b 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. 539 (English).
- ↑ Dean C. Presnall: phase diagrams of Earth-forming minerals . In: TJ Ahrens (Ed.): Mineral Physics & Crystallography - A Handbook of Physical Constants . tape 2 . American Geophysical Union, Washington, DC 1995, p. 248–268 (English, deanpresnall.org ( memento of February 7, 2017 in the Internet Archive ) [PDF; 1.4 MB ; accessed on June 10, 2019]).
- ↑ Localities for forsterite. In: mindat.org. Hudson Institute of Mineralogy, accessed June 10, 2019 .
- ↑ Find location list for forsterite in the Mineralienatlas and Mindat
- ^ Charles A. Poteet, S. Thomas Megeath, Dan M. Watson, Nuria Calvet, Ian S. Remming, Melissa K. McClure, Benjamin A. Sargent, William J. Fischer, Elise Furlan, Lori E. Allen, Jon E. Bjorkman, Lee Hartmann, James Muzerolle, John J. Tobin, Babar Ali: A Spitzer-IRS Detection of Crystalline Silicates in a Protostellar Envelope . In: Astrophysical Journal Letters . 733: L32, no. 2 , 2011, p. 1–6 , doi : 10.1088 / 2041-8205 / 733/2 / L32 , arxiv : 1104.4498v1 (English, iopscience.iop.org [PDF; 335 kB ; accessed on June 10, 2019]).
- ↑ Thomas Henning: Astromineralogy . 2nd Edition. Springer, Berlin, Heidelberg 2010, ISBN 978-3-642-13258-2 .
- ^ A b c 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 .