Microclinic

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Microclinic
Microcline-199473.jpg
Microcline with albite encrustation from papachacra, Departamento Belén, Catamarca, Argentina (size: 9.9 cm × 9.0 cm × 5.3 cm)
General and classification
chemical formula K [AlSi 3 O 8 ]
Mineral class
(and possibly department) 		Silicates and Germanates - framework silicates
System no. to Strunz
and to Dana 		9.FA.30 ( 8th edition : VIII / F.03a)
76.01.01.05
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group C 1 (No. 2, position 3)Template: room group / 2.3
Lattice parameters a  = 8.59  Å ; b  = 12.97 Å; c  = 7.22 Å,
α  = 90.6 °; β  = 116.0 °; γ  = 87.6 °
Formula units Z  = 4
Physical Properties
Mohs hardness 6 to 6.5
Density (g / cm 3 ) measured: 2.54 to 2.57; calculated: 2.56
Cleavage completely according to {001} and {010}
Break ; Tenacity uneven; brittle
colour colorless, white, gray, pink, yellow, red, green
Line color White
transparency transparent to translucent
shine Glass luster, pearlescent luster on the gap surfaces
Crystal optics
Refractive indices n α  = 1.514 to 1.529
n β  = 1.518 to 1.533
n γ  = 1.521 to 1.539
Birefringence δ = 0.007 to 0.010
Optical character biaxial negative
Axis angle 2V = measured: 66 ° to 103 °; calculated: 80 °

Mikroklin is a very common mineral from the group of feldspars within the mineral class of silicates with the idealized chemical composition K [AlSi 3 O 8 ] and is therefore, chemically speaking, a potassium - aluminum- silicate. Structurally Mikroklin one of the framework silicates (tectosilicates).

Mikroklin usually develops prismatic to tabular crystals , but also occurs in the form of granular to massive mineral aggregates . The undamaged surfaces of the transparent to translucent crystals have a glass-like sheen , while cleavage surfaces shimmer more like mother-of-pearl.

Due to its mixed crystal formation with its sodium analogue albite , a portion of the potassium is often replaced ( substituted ) by sodium in the microcline . In addition, various foreign admixtures ensure that microcline is rarely colorless or white due to the formation of twins or lattice construction defects, but often takes on a light yellow, pink to red, blue to green or gray to brown color. The green to blue-green variety amazonite , which is often used as a gemstone due to its play of colors , is known above all .

Etymology and history

Was found for the first time Mikroklin 1830 in Stavern , Norway and described by August Breithaupt , of the minerals by the Greek words μικρός Mikros for "small" and κλίνειν klin for inclined named because of the characteristic that the cleavage planes small deviations show of 90 °.

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the microcline belonged to the mineral class of "silicates and germanates" and there to the department of "tectosilicates (tectosilicates)", where together with anorthoclase , orthoclase and sanidine it belongs to the subgroup the "Kalifeldspate" with the system no. VIII / F.03a within the feldspar family.

In the last revised and updated Lapis mineral directory by Stefan Weiß in 2018 , which, out of consideration for private collectors and institutional collections, is still based on this classic system of Karl Hugo Strunz , the mineral was given the system and mineral number. VIII / J.06-30 . In the "Lapis system" this also corresponds to the department of "framework silicates", where microcline together with buddingtonite , celsian , hexacelsian , hyalophane , kokchetavite , orthoclase, paracelsian , rubiklin , sanidine and slavsonite form an independent but unnamed subgroup within the group of J .06 to J.07 forms the "feldspar group".

The 9th edition of Strunz's mineral systematics , which has been in force since 2001 and updated by the International Mineralogical Association (IMA) until 2009, classifies the microcline in the somewhat differently defined department of “tectosilicates without zeolitic H 2 O”. This is further subdivided according to the possible presence of additional anions , so that the mineral can be found according to its composition in the sub-section "Tectosilicates (tectosilicates) without additional anions", where it can be found together with the intermediate links adulara , anorthoclase and hyalophane as well as buddingtonite, Celsian, Monalbit , Orthoklas, Rubiklin and Sanidin also form the group "Alkalifeldspate" with the system no. 9.FA.30 forms within the feldspar family.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the microcline to the class of "silicates and germanates" and there in the department of "structural silicates with Al-Si lattice". Here he is in the group "K (Na, Ba) -Feldspate" with the system no. 76.01.01 to be found in the subsection " With Al-Si grid ".

Crystal structure

Microcline crystallizes triclinic in space group C 1 (space group no. 2, position 3) with the lattice parameters a  = 8.59  Å ; b  = 12.97 Å; c  = 7.22 Å; α = 90.6 °; β = 116.0 ° and γ = 87.6 ° as well as four formula units per unit cell . Template: room group / 2.3

Varieties and modifications

Amazonite from Yucca Hill, Lake George, Colorado, USA

The compound K [AlSi 3 O 8 ] is dimorphic and, in addition to the triclinic crystallizing low-temperature modification microcline, also occurs as a monoclinic crystallizing high-temperature modification orthoclase .

The only known variety is the light to dark green amazonite .

Education and Locations

Microcline (white) with smoky quartz from Conway, Carroll County, New Hampshire, USA (size: 5.9 cm × 5.9 cm × 3.9 cm)

Microcline forms magmatically in granite , pegmatite and syenite or metamorphically in various rocks . It also forms metamorphoses according to Sanidin .

The accompanying minerals of the microcline include albite , biotite , fluorite , muscovite , quartz , various amphiboles and various tourmalines as well as ore minerals such as spodumene , amblygonite , cassiterite and tantalite (Mn) .

As a frequent mineral formation, microcline can be found in many localities, whereby so far (as of 2015) almost 5000 localities are known.

The Black Hills in the US state of South Dakota, where huge crystals with a diameter of up to 12 meters came to light, are known for their extraordinary microclinic finds. The largest known microclink crystal to date and probably the largest crystal in the world comes from the Devils Hole Beryl Mine in Fremont County of Colorado , where it was discovered in 1981. The crystal is 49.38 meters long, has a cross-section of 35.97 meters × 13.72 meters and weighs 15,908.89 tons.

In Germany, microcline has so far been discovered mainly in the Fichtel Mountains and in Lower Bavaria . In addition, some sites are known in the Black Forest in Baden-Württemberg, near Bad Harzburg in Lower Saxony, near Hochstädten (Bensheim) in Hesse, in the Saxon Ore Mountains and Upper Lusatia as well as in the uranium deposit of Ronneburg in Thuringia.

In Austria, the mineral was found in many places in Carinthia , Lower Austria , in some places in Salzburg , Styria and Upper Austria as well as on Mörchnerkar in Zemmgrund in Tyrol and on Fresch Alp in the Vorarlberg municipality of Silbertal .

Larger areas of discovery include Afghanistan, Argentina, Brazil, China, Canada, Myanmar (Burma), the Czech Republic, Finland, France, Greenland, India, Italy, Japan, Madagascar, Namibia, Norway, the United Kingdom (UK) and the United States of America (USA).

use

Mikroklin is used as a raw material in the ceramic , glass and enamel industries . Its Amazonite variety is used as a gemstone .

See also

literature

Web links

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

Individual evidence

  1. ↑ a b c d e 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.  694 .
  2. ↑ a b The numbering of this axis position does not correspond to the order of the International Tables for Crystallography , because it is not listed there.
  3. ↑ a b c Microcline . 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; 78  kB ; accessed on September 23, 2019]).
  4. ↑ a b c d e Microcline. In: mindat.org. Hudson Institute of Mineralogy, accessed September 23, 2019 .
  5. ↑ 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 .
  6. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed September 23, 2019 .
  7. ↑ Localities for Micro Cline. In: mindat.org. Hudson Institute of Mineralogy, accessed September 23, 2019 .
  8. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Dörfler Natur ). Edition Dörfler im Nebel-Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 264 .
  9. ↑ Mineral Atlas: Mineral Records
  10. ↑ Find location list for microcline in the Mineralienatlas and in Mindat
  11. ↑ 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.  603 .
  12. ^ 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. 180 .