Enstatite

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Enstatite
Enstatite - Kilosa District, Morogoro Region, Tanzania.jpg
Enstatite crystal from Kilosa , Morogoro region, Tanzania (size 1.5 cm × 1.2 cm)
General and classification
other names
  • Amblystegite
  • Chladnite
  • Ficinite
  • Orthoenstatite
  • Paulite
  • Peckhamite
  • Protobastite
  • Shepardite
  • Victorit
chemical formula
  • Mg 2 [Si 2 O 6 ]
  • (Mg, Fe) 2 [Si 2 O 6 ]
Mineral class
(and possibly department) 		Silicates and germanates - chain and band silicates (inosilicates)
System no. to Strunz
and to Dana 		9.DA.05 ( 8th edition : VIII / D.02)
65.01.02.01
Similar minerals Hypersthene
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal; 2 / m  2 / m  2 / m
Space group Pbca (No. 61)Template: room group / 61
Lattice parameters a  = 18.24  Å ; b  = 8.82 Å; c  = 5.18 Å
Formula units Z  = 8
Frequent crystal faces {010}, {210}, {311}, {111}
Twinning simple or lamellar according to {100}
Physical Properties
Mohs hardness 5 to 6
Density (g / cm 3 ) measured: 3.2 to 3.9; calculated: 3.189
Cleavage good after {210}; Secretions according to {100} and {010}
Break ; Tenacity uneven; brittle
colour colorless, white, gray, yellowish green to olive green, brownish
Line color White
transparency translucent to opaque
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.650 to 1.668
n β  = 1.652 to 1.673
n γ  = 1.659 to 1.679
Birefringence δ = 0.009 to 0.011
Optical character biaxial positive
Other properties
Chemical behavior Almost infusible before the soldering tube, insoluble in acids

The enstatite is a common mineral from the group of orthopyroxenes within the mineral class of "silicates and germanates" with the idealized chemical composition of Mg 2 [Si 2 O 6 ]. Enstatite is so chemically seen a magnesium - silicate that is structurally the chain silicates belongs. It forms a mixed series with ferrosilite (Fe 2+ 2 [Si 2 O 6 ]). Within this series, all compositions with more than 1 Mg and less than 0.1 Ca per formula unit are referred to as enstatite, all others generally as hypersthene .

Enstatite is colorless or pale yellow, green, olive or brown in color, transparent to opaque with a glass luster on crystal surfaces and pearlescent luster on cleavage surfaces. The crystals have a prismatic to fibrous habit , often lamellar twinned after {100} and can be up to 50 cm long. It shows good cleavage parallel to the prism surfaces {210}, with the cleavage surfaces intersecting at an angle of 88 °. This distinguishes it from similar amphiboles whose cleavage surfaces intersect at an angle of about 120 °.

Enstatite is a common rock-forming mineral of the earth's mantle ( peridotite ), the lower earth's crust ( granulite ), basic magmatite ( gabbro , pyroxenite ) as well as granulite-facial metabasite (granulite), metapelite and metamorphic calcium silicate rocks. It is also a component of enstatite chondrites and aubrites , rare classes of stone meteorites . This hard mineral has also been found on the surface of some asteroids , such as (44) Nysa , (64) Angelina and (216) Cleopatra .

Etymology and history

The name comes from the Greek ( enstates = opponent, adversary ) and refers to the fact that enstatite is almost infusible.

Other obsolete names were used for enstatite partially or completely converted into other minerals:

  • Agalite: Presumably enstatite partially converted into talc
  • Bastit, Schillerspat: In serpentine , talc and possibly anthophyllite converted enstatite
  • Diaclasite, Germarite, Phastine: transformed enstatite
  • Szaboit: partially transformed enstatite

The mineral was first described and named in 1855 by Gustav Adolf Kenngott . The type locality is the mountain Zdar near Ruda nad Moravou (German Eisenberg an der March ) in the Czech Republic, since the material for chemical analysis came from there.

classification

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

In the 8th edition of the mineral classification according to Strunz , which has been obsolete since 1977 , the enstatite belonged to the mineral class of "silicates and germanates" and there to the department of "chain silicates and band silicates (inosilicates)", where it gave its name to the "enstatite series (orthopyroxene). Rhombic-dipyramidal “with the system no. VIII / D.02 and the other member Hypersthen (discredited as mixed crystal in 1988).

In the Lapis mineral directory according to Stefan Weiß, which, out of consideration for private collectors and institutional collections, is still based on this old form of Karl Hugo Strunz's system , the mineral was given the system and mineral number. VIII / F.02-10 . In the "Lapis system" this also corresponds to the section "Chain silicates and band silicates", where enstatite together with akimotoite , bridgmanite , donpeacorite , ferrosilite , nchwaningite and protoenstatite forms the subgroup of "orthopyroxenes" within the pyroxene group (status 2018).

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and was updated by the International Mineralogical Association (IMA) until 2009, also classifies enstatite under the category of “chain and band silicates (inosilicates)”. However, this 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 sub-section “Chain and band silicates with 2-periodic single chains Si 2 O 6 ; Pyroxene family "can be found, where it is named after the" Orthopyroxene - Enstatite group "with the system no. 9.DA.05 and the other members akimotoite, donpeacorite and ferrosilite.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , also assigns enstatite to the class of "silicates and Germanates" and there in the department of "chain silicate minerals". Here he is together with Ferrosilit 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 ".

Crystal structure

Enstatite under the microscope
Enstatite crystals in tholeiitic basalt from the front Vogelsberg (thin section, LPL)
Enstatite crystals in tholeiitic basalt from the front Vogelsberg (thin section, XPL)

Enstatite crystallizes orthorhombically in the space group Pbca (space group no. 61) with the lattice parameters a  = 18.24  Å ; b  = 8.82 Å; c  = 5.18 Å and 8 formula units per unit cell . Template: room group / 61

The structure is that of orthopyroxes , with layers with opposite orientations of the octahedra alternating after two layers. Silicon (Si 4+ ) occupies the tetrahedral T-positions surrounded by 4 oxygen ions and magnesium (Mg 2+ ) the octahedral M1 and M2-positions surrounded by 6 oxygen.

Under the microscope, enstatite appears in volcanic rocks in the form of colorless to pale green (depending on the Fe content) prisms (with sections parallel to the c-axis) or square or octagonal cross-sections (with sections perpendicular to the c-axis). In plutonites and metamorphites, hypidiomorphic to xenomorphic, granular formations predominate. In polarized light it shows white to orange-colored interference colors of the first order.

Modifications and varieties

Pressure-temperature phase diagram for the compound MgSiO 3 according to Presnell 1995

Magnesium metasilicate MgSiO 3 is polymorphic and can occur with different structure types and symmetries.

Pyroxenes

Enstatite denotes MgSiO 3 with a pyroxene structure in the orthorhombic symmetry described above with the space group Pbca (No. 61) . It is stable at temperatures above ~ 600 ° C and pressures up to ~ 7–12 GPa. At higher pressure, enstatite is transformed into high-line statite with the structure of diopside in the space group C 2 / c (No. 15) . At low pressure below ~ 1 Gpa, enstatite converts above ~ 1000 ° C into the likewise orthorhombic protoenstatite ( Pbcn (No. 60) ). At lower temperatures, the clinoenstatite with the space group ( P 2 1 / c (No. 14) ) is the stable phase. With rapid cooling, protoenstatite does not change into enstatite, but metastable to clinoenstatite at ~ 865 ° C. Template: room group / 61Template: room group / 15Template: room group / 60Template: room group / 14

At low pressure below 1 GPa and temperatures above 1500 ° C, there is still a small stability field of a monoclinic high-temperature clinoenstatite, which melts from ~ 1600–1700 ° C. Enstatite melts at pressures between 1 and 12 GPa and temperatures between 1700 and 2200 ° C.

High pressure phases

The pyroxene structure of MgSiO 3 is no longer stable above 17–18 GPa and the magnesium metasilicate is in the structure of garnet ( majorite ) at temperatures above ~ 1600 ° C and in the ilmenite structure ( akimotoite ) below 1600 to 2000 ° C. At extremely high pressures above ~ 22 GPa, MgSiO 3 changes into the perovskite structure ( bridgmanite ).

Varieties

Bronzite

Well-known varieties are:

  • Bronzite has its iron -Beimengungen a typical bronze color.
  • Lime bronzite is a calcium- containing variety
  • Vanadium bronzite contains admixtures of vanadium

Education and Locations

Enstatite from the Bare Hills Copper Mine, Baltimore County, Maryland, USA (size 9.6 cm × 7.5 cm × 4.9 cm)

Enstatite typically forms in magmatic rocks rich in magnesium and is an essential component of deep rocks such as dunites , gabbros and norites . Together with olivine it forms peridotites and Harzburgites . In volcanic rocks it is found in tholeiites , andesites, and dazites ; it is absent in alkaline rocks . In the case of water scarcity, it can also develop regionally metamorphically in the Katazone, among other things in Charnockites and pyroxen granulites, as well as contact metamorphic in the inner contact area in Pyroxen-Hornfels facies .

In addition to olivine, the accompanying minerals also include diopside , clinopyroxene , phlogopite , pyrope and spinel .

As a frequent mineral formation, enstatite can be found in many places around the world. So far, around 1200 locations for Enstatit have been documented (as of 2020). In addition to its type locality Eisenberg an der March, enstatite was found in several places in Bohemia and Moravia .

In Germany the mineral was found near St. Blasien and Todtmoos in Baden-Württemberg; in Swabia , Franconia and the Upper Palatinate in Bavaria; near Bad Harzburg in Lower Saxony; Niederbachem in North Rhine-Westphalia; in many places in the Eifel in Rhineland-Palatinate as well as near Chemnitz and in the Ore Mountains in Saxony. As a rock-forming mineral , it occurs in numerous places in the tholeiites of the Vogelsberg and the Maintrapps .

In Austria, Enstatit could be found on the Pauliberg in Burgenland, in the Tyrolean community Wildschönau and in several places in Carinthia , Lower Austria , Salzburg and Styria .

In Switzerland, the mineral has so far been found near Utzenstorf (Bern), Tafers (Friborg), Châtillens (Waadt), Saas-Almagell (Valais) and in several places in the cantons of Graubünden and Ticino .

Other locations are Algeria , Antarctica , Argentina , Azerbaijan , Australia , Botswana , Brazil , Chile , China , Finland , France , Ghana , Greece , Greenland , India , Israel , Italy , Japan , Yemen , Canada , Kazakhstan , Lesotho , Libya , Madagascar , Mexico , Mongolia , Myanmar , Namibia , New Caledonia , New Zealand , Nigeria , Norway , Oman , Pakistan , Papua New Guinea , Peru , Poland , Portugal , Republic of the Congo , Romania , Russia , in the Western Sahara , on the Solomon Islands , Sweden , Zimbabwe , Slovakia , Spain , Sudan , South Africa , Tajikistan , Tanzania , Czech Republic , Turkey , Ukraine , Hungary , the United Kingdom (Great Britain) and the United States of America (USA).

Enstatite was also found in rock samples from the Mid-Atlantic Ridge and East Pacific Ridge as well as outside the Earth on the moon (landing site of the Apollo 15 mission) and in the tail material of Comet Wild 2 .

Locations for the bronzite variety include various meteorites near Massing (Bavaria), Breitscheid (Hesse) , Ibbenbüren and Peckelsheim (North Rhine-Westphalia) and the Ölberg near Hundsangen (Rhineland-Palatinate) and Freiberg (Saxony) in Germany; the Totenkopf (Salzburg) and the Hohenwartberg in the Dunkelsteinerwald (Lower Austria) as well as Kraubath an der Mur (Styria) in Austria and in various meteorites near Utzenstorf (Bern), Langwies (Graubünden) and Châtillens (Vaud) in Switzerland.

use

Pure enstatite stones can be used as highly refractory stone.

Clear varieties that are worth grinding are also often processed into gemstones .

See also

literature

  • Adolf Kenngott: Mineralogical notes concerning the known species: karstenite, dolomite, millerite, tourmaline, galactite, water, plagionite, diopside, zincite, calcite and Felsöbanyt, as well as two new ones: the enstatite in the sex of the Augit-Spathe and the pseudophite in the sex the serpentine steatite . In: Meeting reports of the Imperial Academy of Sciences . tape 16 , 1855, pp. 152–179 ( rruff.info [PDF; 1.6 MB ; accessed on August 13, 2018]).
  • Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 232 .

Web links

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

Individual evidence

  1. ↑ a b 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 .
  2. ↑ Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: January 2020. (PDF 1729 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, January 2020, accessed February 26, 2020 .
  3. ↑ a b c d 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.  619 (English).
  4. ↑ a b c d e f Enstatite . 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 February 26, 2020]).
  5. ↑ a b c d Enstatite. In: mindat.org. Hudson Institute of Mineralogy, accessed February 26, 2020 .
  6. ↑ Adolf Kenngott: About the Enstatite, a new species in the Augit-Spathe family . In: Meeting reports of the Imperial Academy of Sciences . tape 16 , March 15, 1855, p. 162 ( rruff.info [PDF; 1.6 MB ; accessed on February 26, 2020]).
  7. ↑ Subcommite on Pyroxenes, CNMMN; Nobuo Morimoto: Nomenclature of Pyroxenes . In: The Canadian Mineralogist . tape 27 , no. 1 , 1989, pp. 143–156 ( rruff.info [PDF; 1.1 MB ; accessed on February 26, 2020]).
  8. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1816 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed February 26, 2020 .
  9. ↑ a b BE Warren and DI model: The structure of enstatite MgSiO3 . In: Journal of Crystallography . tape 75 , 1930, pp. 1–14 ( rruff.info [PDF; 1.7 MB ; accessed on February 29, 2020]).
  10. ↑ Hans Pichler, Cornelia Schmitt-Riegraf: Rock -forming minerals in thin sections . 2nd Edition. Enke, Stuttgart 1993, ISBN 3-8274-1260-9 , pp. 84-87 .
  11. ↑ a b c Dean C. Presnall: Phase Diagrams of Earth-Forming Minerals . In: Mineral physics and crystallography: a handbook of physical constants . 1995, p. 252-273 ( citeseerx.ist.psu.edu [PDF; 24.1 MB ; accessed on May 19, 2019]).
  12. ^ Leon Atlas: The Polymorphism of MgSiO3 and Solid-State Equilibria in the System MgSiO 3 -CaMgSi 2 O 6 . In: The Journal of Geology . tape 60 , 1952, pp. 125-147 , doi : 10.1086 / 625944 .
  13. ^ JF Sarver, FA Hummel: Stability Relations of Magnesium Metasilicate Polymorphs . In: Journal of the American Ceramic Society . tape 45 , 1962, pp. 152-156 , doi : 10.1111 / j.1151-2916.1962.tb11110.x .
  14. ↑ a b 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.  510 .
  15. ↑ Roland Vinx: Rock determination in the field . 3. Edition. Spectrum, Heidelberg 2011, ISBN 978-3-8274-2748-9 , p. 78 .
  16. ^ Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  755-756 .
  17. ↑ Localities for Enstatite. In: mindat.org. Hudson Institute of Mineralogy, accessed February 26, 2020 .
  18. ↑ Thomas Reischmann, Adalbert Schraft: The Vogelsberg - Geotopes in the largest volcanic area in Central Europe . Ed .: Hessian State Office for Environment and Geology. Wiesbaden 2009, p. 16 .
  19. ↑ Hans Pfisterer: The basalts of the southwestern Vogelsberg to the right of the Main line . In: New yearbook for mineralogy, geology and paleontology, supplement volume . tape 40 , 1916, pp. 1-50 .
  20. ↑ a b Locations for enstatite at the Mineralienatlas and at Mindat , accessed on February 26, 2020.
  21. ↑ Localities for Bronzite. In: mindat.org. Hudson Institute of Mineralogy, accessed February 26, 2020 .
  22. ^ 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. 208 .
  23. ↑ Michael RW Peters: Enstatit. In: realgems.org. December 26, 2010, accessed February 26, 2020 (with image examples of cut Enstatites).