Clinoferrosilite

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Clinoferrosilite
General and classification
other names

Clinoferrosilit, Ferropigeonit, Clinoeulit, Clinohypersthen

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.10 ( 8th edition : 8 / F.01-20)
65.1.1.2
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / c (No. 14)Template: room group / 14
Lattice parameters a  = natural: 9.718; synthetic: 9.7075 (5)  Å ; b  = natural: 9.088; synthetic: 9.0807 (4) Å; c  = natural: 5.239; synthetic: 5.2347 (5) Å
α  = 90 °; β  = natural: 108 ° 27 '; synthetic: 108.46 °; γ  = 90 °
Formula units Z  = 4
Physical Properties
Mohs hardness 5-6
Density (g / cm 3 ) Please complete!
Cleavage Please complete!
Break ; Tenacity uneven, splintery
colour natural: pale beige, colorless to brown or green
Line color Please complete!
transparency transparent
shine Please complete!
radioactivity -
Crystal optics
Refractive indices n α  = natural: 1.763 (2)
n γ  = natural: 1.794 (2)
Birefringence δ = natural: 0.031
Optical character biaxial positive
Axis angle 2V = measured: 25 °, calculated: 40 °

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

Clinoferrosilite crystallizes with monoclinic symmetry and forms pale beige to green, needle-like crystals less than one millimeter in size.

The type locality is the obsidian of the Obsidian Cliff in Park County (Wyoming) , USA .

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. Further investigations by Bowen and Posnjak, which confirmed this, had just been published when, in late 1935, NL Bowen identified monoclinic crystals with the optical properties of pure ferrosilite in an obsidian from Lake Naivasha in Kenya . Since it was the monoclinic form of ferrosilite, he suggested the name clinoferrosilite. A direct determination of the structure and composition of these very small crystals was not possible with the analytical possibilities of the 1930s and so it was not until 1965 that the existence of this clinopyroxene was confirmed by MG Bown in Cambridge. Later experimental investigations showed that the clinoferrosilites from obsidians are metastable formations.

classification

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

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the clinoferrosilite belonged to the department of " chain and band silicates (inosilicates) ", where it together with aegirine , augite , diopside , essenite , hedenbergite , jadeite , jervisite , johannsenite , Kanoite , Klinoenstatite , Kosmochlor , Namansilit , Natalyit , Omphacit , Petedunnit , Pigeonit and Spodumene the "Pyroxene group, subgroup Klinopyroxene" 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 assigns clinoferrosilite 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 Kanoite, Klinoenstatite, and Pigeonit the" Mg, Fe, Mn-Klinopyroxene - Klinoenstatite group "with the system no. 9.DA.10 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns clinoferrosilite to the class of "silicates and Germanates" and there in the department of "chain silicate minerals". Here it is together with Klinoenstatit, Kanoit and Pigeonit in the group of "P2 / c Klinopyroxene" with the system no. 65.01.01 can be found in the subsection " Chain Silicates: Simple unbranched chains, W = 1 with chains P = 2 ".

Chemism

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

Klinoferrosilit forms a complete series of mixtures with clinoenstatite according to the exchange reaction

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

All clinoenstatite-clinoferrosilite mixed crystals with more than 50% Fe 2+ on the octahedral positions M1 and M2 are called clinoferrosilite , whereby the iron-rich compounds of this mixture series are only stable at high pressure (> ~ 10 kbar).

The clinoferrosilite investigated by Bowen in 1935 and Bown in 1965 contains ~ 5 mol% kanoite, corresponding to the exchange reaction

  • [M1.2] Fe 2+ = [M1.2] Mn 2+ (Kanoite).

Crystal structure

Clinoferrosilite crystallizes with monoclinic symmetry in the space group P 2 1 / c (space group no. 14) with 4 formula units per unit cell . The synthetic end  link has the lattice parameters a = 9.7075 (5)  Å , b  = 9.0807 (4) Å, c  = 5.2347 (5) Å and β = 108.46 °. Template: room group / 14

The structure is that of clinopyroxene . Silicon (Si 4+ ) occupies the tetrahedral T-positions surrounded by 4 oxygen ions and iron (Fe 2+ ) the octahedral M1 and M2 positions surrounded by 6 oxygen.

Modifications

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

Pyroxenes

Clinoferrosilite denotes FeSiO 3 with a pyroxene structure and monoclinic symmetry in the space group P 2 1 / c (No. 14) and is stable at high pressure between ~ 1 GPa and ~ 5 GPa and temperatures below 800 ° C. At 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

At extremely high pressures above 30-36 GPa, clinoferrosilite with the symmetry C2 / c changes into a new structure with the space group P 2 1 / c (no. 14) , which is characterized by the partially octahedral coordination of the silicon. Such as B. in the SiO 2 high pressure modification stishovite silicon is then surrounded by 6 instead of normally 4 oxygen. Template: room group / 14

Above 800 ° C, clinoferrosilite transforms into ferrosilite with orthorhombic symmetry in the space group Pbca (No. 61) and the structure of the pyroxene enstatite . Template: room group / 61

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

Pure clinoferrosilite 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 and clinoferrosilite at higher temperatures or lower pressures. Incorporation of calcium or aluminum favor the formation of clinoferrosilite instead of ferrosilite.

Clinoferrosilite is often metastable outside this stability range. The first description comes from an obsidian from Lake Naivasha in Kenya , where it occurs together with anorthoclase , cristobalite , magnetite , fayalite and biotite in a rhyolite obsidian. The type locality is the obsidian of the Obsidian Cliff in Park County (Wyoming) , USA.

Web links

Individual evidence

  1. ^ IMA Database of Mineral Properties - Clinoferrosilite. In: rruff.info. RRUFF Project in partnership with the IMA, accessed April 30, 2019 .
  2. ↑ a b c d e f g h Clinoferrosilite. In: mindat.org. Hudson Institute of Mineralogy, accessed June 2, 2019 .
  3. ^ A b c MG Bown: Re-investigation of clino-ferrosilite from Lake Naivasha, Kenya . In: Mineralogical Magazine . tape 34 , 1965, pp. 66–70 ( rruff.info [PDF; 256 kB ; accessed on June 2, 2019]).
  4. ^ A b c d 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 June 2, 2019]).
  5. ↑ a b c d e f g h 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]).
  6. ↑ a b List of locations for clinoferrosilite in the Mineralienatlas and Mindat
  7. ↑ NFM Henry: Some data on the iron-rich hyper Demosthenes . In: Mineralogical Magazine . tape 24 , 1935, pp. 221–226 ( rruff.info [PDF; 226 kB ; accessed on June 2, 2019]).
  8. ^ NL Bowen, JF Schairer: The system, FeO-SiO 2 . In: American Journal of Science . tape 24 , 1932, pp. 177-213 , doi : 10.2475 / ajs.s5-24.141.177 .
  9. ↑ a b c Douglas Smith: Stability of iron-rich pyroxene in the system CaSiO 3 -FeSiO 3 -MgSiO 3 . In: American Mineralogist . tape 57 , 1972, p. 1413–1428 ( minsocam.org [PDF; 1.1 MB ; accessed on June 2, 2019]).
  10. ↑ 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 June 2, 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 ( deepblue.lib.umich.edu [PDF; 774 kB ; accessed on June 2, 2019]).
  12. ↑ Anna Pakhomova, Leyla Ismailova, Elena Bykova, Maxim Bykov, Tiziana Boffa Ballaran, Leonid Dubrovinsky: A new high-pressure phase transition in clinoferrosilite: In situ single-crystal X-ray diffraction study . In: American Mineralogist . tape 103 , 2017, p. 666-673 , doi : 10.2138 / am-2017-5853 .
  13. ↑ Natalia V. Solomatova, Ayya Alieva, Gregory J. Finkelstein, Wolfgang Sturhahn, Michael B. Baker, Christine M. Beavers, Jiyong Zhao, Thomas S. Toellner, Jennifer M. Jackson: High-pressure single-crystal X-ray diffraction and synchrotron Mössbauer study of monoclinic ferrosilite . In: Comptes Rendus Geoscience . tape 351 , 2019, p. 129–140 , doi : 10.1016 / j.crte.2018.06.012 .
  14. ^ Hans-Peter Weber: Ferrosilite III, the high-temperature polymorph of FeSiO 3 . In: Acta Crystallographica . C39, 1983, pp. 1–3 , doi : 10.1107 / S010827018300339X ( brief description available online at scripts.iucr.org ).