Ferrosilite

from Wikipedia, the free encyclopedia
Ferrosilite
Ferrosilite-111338.jpg
Needle ferrosilite from Lake Tarawera in the Bay of Plenty region , North Island, New Zealand
General and classification
other names

Orthoferrosilite, eulysite, eulite, hypersthene, iron hypersthene

chemical formula Fe 2+ 2 Si 2 O 6
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.DA.05 ( 8th edition : 8 / F.02-20)
65.1.2.2
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol mmmTemplate: crystal class / unknown crystal class
Space group Pbca (No. 61)Template: room group / 61
Lattice parameters a  = natural: 18.42; synthetic: 18.417 (2)  Å ; b  = natural: 9.050; synthetic: 9.078 (1) Å; c  = natural: 5.241; synthetic: 5.2366 (4) Å
α  = 90 °; β  = 90 °; γ  = 90 °
Formula units Z  = 8
Physical Properties
Mohs hardness 5-6
Density (g / cm 3 ) of course: 3.84
Cleavage {210}, (010), (100)
Break ; Tenacity uneven, splintery
colour of course: green, brown
Line color pale gray-brown
transparency transparent
shine Glass gloss
radioactivity -
magnetism paramagnetic
Crystal optics
Refractive indices n α  = natural: 1.765 synthetic: 1.772
n β  = natural: 1.774 synthetic: 1.780
n γ  = natural: 1.786 synthetic: 1.789
Birefringence δ = natural: 0.020; synthetic: 0.017
Optical character biaxial positive
Axis angle 2V = natural: 79 °, synthetic: 58 °, 86 °
Pleochroism natural: inconsistent weak (yellowish - weak green) to strong (beige - green-gray), pale pink, pink-yellow, pale blue-green

The mineral ferrosilite is a rare chain silicate from the pyroxene group with the idealized chemical composition Fe 2+ 2 Si 2 O 6 .

Ferrosilite crystallizes with orthorhombic symmetry and forms brown to green, mostly irregularly granular, more rarely prismatic, long-tabular to needle-like crystals a few millimeters in size.

Ferrosilite is formed under the conditions of the lower earth's crust (~ 30 km depth) and is found worldwide in basic igneous rocks and metamorphic rocks with a high iron : magnesium ratio, e.g. B. Charnockites and metamorphic iron ores.

Etymology and history

The first iron-rich hypersthene was found in Vittinki near Seinäjoki in Finland and described by M. Saxen in 1925. The name ferrosilite for the iron (ferro) metasilicate (silite) FeSiO 3 was introduced by Henry Stephens Washington in 1932. In the same year, Norman L. Bowen and John Frank Schairer published their study of FeO-SiO 2 compounds at ambient pressure and showed that ferrosilite is not a stable compound under the conditions investigated. In the following years no hypersthenes with more than 85 mol% ferrosilite were found in nature either. After all, it was Bowen himself who in late 1935 identified a monoclinic pyroxene with the optical properties of pure ferrosilite in an obsidian from Lake Naivasha in Kenya and named it clinoferrosilite. Later investigations showed that the clinoferrosilites from obsidians are metastable formations.

It was not until 1964 that working groups in Japan and at the Geophysical Laboratory of the Carnegie Institution of Washington, which Henry Stephens Washington helped to initiate, could experimentally prove that ferrosilite is a stable mineral at high pressure.

The first complete description of a natural, orthorhombic ferrosilite with almost terminal composition from a pyroxene gneiss of the Mount Marcy area in the Adirondack Mountains was published by Howard W. Jaffe and co-workers in 1978.

classification

In the structural classification of the International Mineralogical Association (IMA) ferrosilite belongs together with enstatite , protoenstatite , clino , Klinoferrosilit and pigeonite to the magnesium-iron Proxenen (Mg-Fe pyroxenes) in pyroxene .

In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of ferrosilite belonged to the mineral class of "silicates and Germanates" and then to the Department of "chain silicates and band silicates (inosilicates)" where he collaborated with Donpeacorite , enstatite and Nchwaningit the independent subgroup of "Orthopyroxene" within the Pyroxengruppe 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 assigns ferrosilite to the class of "silicates and germanates" and there in the department of "chain and band silicates (inosilicates)" a. This department is further subdivided according to the structure of the silicate chains as well as belonging to larger mineral families, so that the mineral according to its composition and structure is classified in the subdivision “Chain and band silicates with 2-periodic single chains Si 2 O 6 ; Pyroxene family "is to be found, where together with akimotoite , donpeacorite and enstatite the" orthopyroxene - enstatite group "with the system no. 9.DA.05 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking area , also assigns ferrosilite to the class of "silicates and Germanates" and there in the department of "chain silicate minerals". Here he is together with Enstatit and Donpeacorit in the group of "Orthopyroxene" with the system no. 65.01.02 within the subsection " Chain Silicates: Simple unbranched chains, W = 1 with chains P = 2 ".

Chemism

Ferrosilite has the idealized composition [M2] Fe 2+ [M1] Fe 2+ [T] Si 2 O 6 is the iron analog of enstatite ( [M2] Mg [M1] Mg [T] Si 2 O 6 ), where [M2], [M1] and [T] are the positions in the pyroxene structure .

Ferrosilit forms a complete series of mixtures with enstatite according to the exchange reaction

  • [M1.2] Fe 2+ = [M1.2] Mg 2+ (enstatite).

All enstatite-ferrosilite mixed crystals with more than 50% Fe 2+ on the octahedral positions M1 and M2 are called ferrosilite , whereby the iron-rich compounds of this mixture series are only stable at high pressure (> ~ 10 kbar). The separate names for the intermediate compositions, ferrohypersthen (50-70 mol% ferrosilite), eulite (70-90 mol% ferrosilite), orthoferrosilite (90-100 mol% ferrosilite), were discarded in 1989.

In the ferrosilite - hedenbergite series there is a large, asymmetrical miscibility gap and ferrosilite does not incorporate more than ~ 5 mol% of hedenbergite ( [M2] Ca 2+ [M1] Fe 2+ [T] Si 2 O 6 ) , even at high temperatures , according to the exchange reaction

  • [M2] Fe 2+ = [M2] Ca 2+ (hedenbergite).

Hedenbergite, on the other hand, has a more extensive miscibility with ferrosilite ranging from 20 mol% at 800 ° C, 20 kbar to 80 mol% ferrosilite at ~ 1000 ° C.

Crystal structure

Ferrosilite crystallizes with orthorhombic symmetry in the space group Pbca (space group no. 61) with 8 formula units per unit cell . The synthetic end  link has the lattice parameters a = 18.417 (2)  Å , b  = 9.078 (1) Å and c  = 5.2366 (4) Å. Template: room group / 61

The structure is that of orthopyroxene . Silicon (Si 4+ ) occupies the two symmetrically different T-positions which are tetrahedrally surrounded by 4 oxygen ions and which are each linked to form symmetrically different single chains. Iron (Fe 2+ ) occupies the M1 and M2 positions , which are octahedrally surrounded by 6 oxygen.

The metal-oxygen bonds have a clear covalent component and the charge of the cations, determined by X-ray analysis, is lower than the ideal ion charge:

  • Si: +2.25
  • Fe: +1.12

Modifications

The compound FeSiO 3 is polymorphic and can occur with different structure types and symmetries.

Pyroxenes

Ferrosilite refers to FeSiO 3 with a pyroxene structure and orthorhombic symmetry in the space group Pbca (No. 61) and is stable at high pressure between ~ 1 GPa and ~ 4-7 GPa and temperatures above 800 ° C. Incorporation of magnesium or manganese expands the stability range to lower pressure and higher temperatures. Template: room group / 61

At room temperature and very high pressures, ferrosilite (α-orthopyroxene) first transforms metastably into monoclinic β-orthopyroxene (~ 10 GPa), then into orthorhombic γ-orthopyroxene (~ 12 GPa).

Below 800 ° C ferrosilite transforms into clinoferrosilite with monoclinic symmetry in the space group P 2 1 / c (No. 14) and the structure of pyroxene pigeonite . At very high pressure of ~ 1.8 GPa at 20 ° C or 4-5 GPa at 800 ° C, the symmetry changes and clinoferrosilite is present in the structure of augite with the space group C 2 / c (No. 15) . Orthorhombic ferrosilite also converts into this structure at temperatures above ~ 800-1200 ° C and pressures above ~ 4-7 GPa. Template: room group / 14Template: room group / 15

Pyroxenoids

At temperatures above 1000 ° C, FeSiO 3 is present as a triclinic single chain silicate with a periodicity of 9 (ferrosilite III). It was synthesized at 2 GPa and 1250 ° C.

The unbranched sevens single chain silicate Pyroxferroit also has the nominal composition FeSiO 3 , but always contains small amounts of manganese and calcium .

Education and Locations

Ferrosilite (hypersthene)

Pure ferrosilite is stable at medium to high pressure and breaks down below ~ 10 kBar to fayalite (Fe 2 SiO 4 ) and quartz (SiO 2 ). Incorporation of magnesium or manganese increases the stability range of ferrosilite at higher temperatures or lower pressures.

Ferrosilite crystallizes under the conditions of the lower earth's crust at a depth of ~ 30 km and is found worldwide in basic igneous rocks, e.g. B. charnockites , granulites and metamorphic iron-rich sediments, e.g. B. band ore or submarine deposits of hydrothermal origin and in some meteorites.

Web links

Commons : Ferrosilite  - collection of images, videos and audio files

Individual evidence

  1. ^ IMA Database of Mineral Properties - Ferrosilite. In: rruff.info. RRUFF Project in partnership with the IMA, accessed March 30, 2019 .
  2. ↑ a b c d e f g h Ferrosilite. In: mindat.org. Hudson Institute of Mineralogy, accessed April 7, 2019 .
  3. ↑ a b c d e f g h i j k l m n o Howard W. Jaffe, Peter Robinson and Robert T. Tracy: Orthoferrosilite and other iron-rich pyroxenes in microperthite gneiss of the Mount Marcy area, Adirondack Mountains . In: American Mineralogist . tape 63 , 1978, pp. 1116–1136 ( minsocam.org [PDF; 2.3 MB ; accessed on April 26, 2019]).
  4. ↑ a b c Shigeho Sueno, Mary Ellen Cameron, CT Prewitt: Orthoferrosilite: High-temperature crystal chemistry . In: American Mineralogist . tape 61 , 1976, p. 38–53 ( rruff.info [PDF; 1.6 MB ; accessed on March 31, 2019]).
  5. ↑ a b c d e f g h i j NFM Henry: Some data on the iron-rich hypersthenes . In: Mineralogical Magazine . tape 24 , 1935, pp. 221–226 ( rruff.info [PDF; 226 kB ; accessed on March 31, 2019]).
  6. ↑ a b c d e f DH Lindsley, BTC Davis, ID Macgregor: Ferrosilite (FeSiO3): Synthesis at High Pressures and Temperatures . In: Science . tape 144 , 1964, pp. 73-74 , doi : 10.1126 / science.144.3614.73 .
  7. ↑ a b NL Bowen: “Ferrosilite” as a natural mineral . In: American Journal of Science . tape 30 , 1935, pp. 481–494 ( rruff.info [PDF; 830 kB ; accessed on March 31, 2019]).
  8. ^ NL Bowen and JF Schairer: The system, FeO-SiO2 . In: American Journal of Science . tape 24 , 1932, pp. 177-213 , doi : 10.2475 / ajs.s5-24.141.177 .
  9. ↑ Syun-iti AKIMOTO, Hideyuki FUJISAWA and Takashi KATSURA: Synthesis of FeSiO3 Pyroxene (Ferrosilite) at High Pressures . In: Proceedings of the Japan Academy . tape 40 , 1964, pp. 272–275 ( jst.go.jp [PDF; 278 kB ; accessed on April 26, 2019]).
  10. ↑ a b Subcommite on Pyroxenes, CNMMN; Nobuo Morimoto: Nomenclature of Pyroxenes . In: The Canadian Mineralogist . tape 27 , 1989, pp. 143–156 ( mineralogicalassociation.ca [PDF; 1.6 MB ; accessed on March 30, 2019]).
  11. ^ A b Steven R. Bohlen, Eric J. Essene, AL Boettcher: REINVESTIGATION AND APPLICATION OF OLIVINE-QUARTZ-ORTHOPYROXENE BAROMETRY . In: Earth and Planetary Science Letters . tape 47 , 1980, pp. 1–10 ( umich.edu [PDF; 774 kB ; accessed on April 26, 2019]).
  12. ^ A b DH Lindleyand JL Munoz: Subsolidus Relations Along The Join Hedenbergite-Ferrosilite . In: American Journal of Science . 267-A, 1969, pp. 295–324 ( yale.edu [PDF; 1.6 MB ; accessed on April 26, 2019]).
  13. ^ Charles W. Burnham, Yoshikazu Ohashi, Stefan S. Hafner, David Virgo: Cation distribution and atomic thermal vibrations in an iron-rich orthopyroxene . In: American Mineralogist . tape 56 , 1971, p. 850–876 ( rruff.info [PDF; 1.9 MB ; accessed on March 31, 2019]).
  14. ↑ Joseph R. Smyth: At orthopyroxenes Structure Up to 850 ° C . In: American Mineralogist . tape 58 , 1973, p. 636–648 ( rruff.info [PDF; 1.4 MB ; accessed on April 26, 2019]).
  15. ↑ Satoshi Sasaki, Yoshio Takeuchi, Kiyoshi Fujino and Syun-iti Akimoto: Electron-density distributions of three Orthopyroxenes, Mg2Si2O6, Co2Si2O6 and Fe2Si2O6 . In: Journal of Crystallography . tape 158 , 1982, pp. 279-297 , doi : 10.1524 / zkri.1982.158.12.279 .
  16. ^ A b DA Hugh-Jones, AB Woodland, RJ Angel: The structure of high-pressure C2 / c ferrosilite and crystal chemistry of high-pressure C2 / c pyroxene . In: American Mineralogist . tape 79 , 1994, pp. 1032-1041 ( minsocam.org [PDF; 1.3 MB ; accessed on April 28, 2019]).
  17. ↑ Przemyslaw Dera, Gregory J. Finkelstein, Thomas S. Duffy, Robert T. Downs, Yue Meng, Vitali Prakapenka, Sergey Tkachev: Metastable high-pressure transformations of orthoferrosilite Fs82 . In: Physics of the Earth and Planetary Interiors . in press, 2013, p. 1–7 ( rruff.info [PDF; 733 kB ; accessed on April 28, 2019]).
  18. ^ Hans-Peter Weber: Ferrosilite III, the high-temperature polymorph of FeSiO3 . In: Acta Crystallographica . C39, 1983, pp. 1-3 , doi : 10.1107 / S010827018300339X ( iucr.org ).
  19. ^ A b RA Howie: CELL PARAMETERS OF ORTHOPYROXENES . In: MINERALOGICAL SOCIETY OF AMERICA, SPECIAL PAPER . tape 1 , 1963, p. 213–222 ( rruff.info [PDF; 8.0 MB ; accessed on April 30, 2019]).
  20. ↑ Dag Eigil Ormaasen: Petrology of the Hopen mangerite-charnockite intrusion, Lofoten, north Norway . In: Lithos . tape 10 , 1977, pp. 291-310 , doi : 10.1016 / 0024-4937 (77) 90004-4 .
  21. ↑ Kazuo Tsuru and NFM Henry: An iron-rich optically-positive hypersthene from Manchuria. In: Mineralogical Magazine . tape 24 , 1937, pp. 527-528 ( rruff.info [PDF; 81 kB ; accessed on April 30, 2019]).
  22. ↑ Cornelis Klein, Jr .: Mineralogy and Petrology of the Metamorphosed Wabush Iron Formation, Southwestern Labrador . In: Journal of Petrology . tape 7 , 1966, pp. 246-305 , doi : 10.1093 / petrology / 7.2.246 .
  23. ↑ Cornelis Klein: Regional metamorphism of Proterozoic iron-formation, Labrador Trough, Canada . In: American Mineralogist . tape 63 , 1978, pp. 898-912 ( minsocam.org [PDF; 1.8 MB ; accessed on April 30, 2019]).
  24. ↑ Franco Mancini, Reijo Alviola, Brian Marshall, Hisao Satoh, Heikki Papunen: The manganese silicate rocks of the early Proterozoic Vittinki group, southwestern Finland: Metamorphic grade and genetic interpretations . In: The Canadian Mineralogist . tape 38 , 2000, pp. 1103–1124 ( rruff.info [PDF; 6.2 MB ; accessed on April 30, 2019]).
  25. ↑ Find location list for ferrosilite in the Mineralienatlas and Mindat