Albite

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Albite
Albite-70858.jpg
Albite crystal group from the Val Chisone , Turin, Piedmont, Italy (size: 2.4 × 1.7 × 1.1 cm)
General and classification
other names

Soda feldspar

chemical formula Na [AlSi 3 O 8 ]
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.FA.35 ( 8th edition : VIII / J.07)
76.01.03.01
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 see crystal structure
Frequent crystal faces {001}, {010}, {110}, {1 1 0}, {10 1 } and others
Twinning often according to the "Albit law", "Periclin law"
Physical Properties
Mohs hardness 6 to 6.5
Density (g / cm 3 ) measured: 2.60 to 2.65; calculated: 2.609 to 2.621
Cleavage perfect after {001}, imperfect, after {110}, very good after {010}
Break ; Tenacity uneven to shell-like; brittle
colour colorless, white, gray, yellow, red, green, blue
Line color White
transparency transparent to translucent
shine Glass luster, pearlescent luster on cleavage surfaces
Crystal optics
Refractive indices n α  = 1.528 to 1.533
n β  = 1.532 to 1.537
n γ  = 1.538 to 1.542
Birefringence δ = 0.010
Optical character biaxial positive
Axis angle 2V = 45 °

Albite or soda feldspar is a very common mineral from the mineral class of " silicates and germanates ". It crystallizes in the triclinic crystal system with the idealized chemical composition Na [AlSi 3 O 8 ], so it is a sodium - aluminum silicate. Structurally it belongs to the framework silicates (tectosilicates).

Albite belongs to the large family of feldspars and forms the sodium-rich end member of the mixed crystal series or the three-component system orthoclase  (K [AlSi 3 O 8 ]) - albite -  anorthite  (Ca [Al 2 Si 2 O 8 ]) in the plagioclase group the intermediate links oligoclase , andesine , labradorite and bytownite . Due to the mixed crystal formation, the formula for sodium-rich plagioclase feldspars is generally also given as (Na, Ca) [(Si, Al) 4 O 8 ]. Since the mixed crystals cannot be macroscopically differentiated, they were arbitrarily divided according to increasing anorthite content, whereby albite may be designated as such if it contains a maximum of 10% anorthite.

Albite mainly develops flat, tabular to prismatic crystals and twins , whereby polysynthetic twins can usually be recognized by their striped crystal surfaces. Granular to massive mineral aggregates are also known . In its pure form, albite is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline formation, it can also appear white or, due to foreign admixtures, it can take on a gray, yellowish, reddish, greenish or bluish color, the transparency decreasing accordingly. Clear and undamaged crystal surfaces have a glass-like sheen , whereas cleavage surfaces have a mother-of-pearl shimmer .

Etymology and history

Albite was first scientifically described in 1815 by Johan Gottlieb Gahn and Jöns Jakob Berzelius , who named the mineral after the Latin word albus for "white" because of its predominantly white color .

The type locality is the "Finnbo" quartz and pegmatite quarry near Falun in the Swedish province of Dalarnas County .

classification

Already in the outdated, but occasionally still used 8th edition of the mineral classification by Strunz albite belonged to the mineral class of "silicates and Germanates" and there to the general ward of the " framework silicates (tectosilicates)", where he was a member of the subgroup of "plagioclase" with the system no. VIII / J.07 can be found within the feldspar group.

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), classifies albite in the more finely subdivided division 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 is found together with anorthite , the intermediate links andesine , bytownite , labradorite and oligoclase the subgroup of "plagioclase" with the system no. 9.FA.35 forms. The mineral reed mergnerite is also assigned to this group .

The systematics of minerals according to Dana also assigns albite to the class of "silicates and germanates" and there into the department of "framework silicates: Al-Si lattice". Here it is also in the "plagioclase series" with system no. 76.01.03 to be found in the sub-section " With (simple) Al-Si grid ".

Crystal structure

Albite crystal from Greece looking in the direction of the b-axis

Two structural modifications of albite are known, both of which crystallize in the triclinic crystal system in space group C 1 (space group no. 2, position 3) with slightly different lattice parameters . With four formula units per unit cell, the lattice parameters are for Template: room group / 2.3

  • High albite : a  = 8.16  Å ; b  = 12.88 Å; c  = 7.11 Å; α = 93.5 °; β = 116.5 ° and γ = 90.2 °
  • Deep albite : a  = 8.14  Å ; b  = 12.79 Å; c  = 7.16 Å; α = 94.2 °; β = 116.6 ° and γ = 87.7 °

Deep albite can be converted into high albite by heating to over approx. 700 ° C; The term anal bit is sometimes used for high albite . Further heating of high albite to over 1050 ° C leads to a conversion of the triclinic into a monoclinic structure. This modification is also known as the monal bit .

properties

morphology

Scheme of possible crystal twins in albite

Albite predominantly forms crystal twins in the form of lamellar repetitive twins , which are noticeable through their characteristic stripes on the crystal surfaces. Two twin laws are preferred, one of which is named after the albite.

In the “Albit Law”, the b-area (010) forms the cohesion level of the twins. At the base there is a re-entrant angle of 7 ° 12 'to 8 ° 20'. The “cleavage surface” c, but also all other surfaces (with the exception of b), are longitudinally striped by a lamellar repetition of this law. Due to the twin stripes characteristic of all plagioclases, these can be relatively easily distinguished from the potash feldspars in the rock. However, these are usually only visible under the microscope.

In the “periclin law”, the twin axis is parallel to the b-axis [010]. The surface of the intergrowth is here either the base, with the twin halves overlapping, or the so-called "X-surface" or the "rhombic cut", in which the two twin halves fit together. Depending on the composition of the plagioclase, the "rhombic section" changes its position in relation to the crystallographic axes and can therefore be used for their optical determination.

Chemical properties

Albite dissolves easily in hydrofluoric acid (HF) but difficult to dissolve in hydrochloric acid (HCl), oxalic acid, and dilute sulfuric acid (H 2 SO 4 ).

Modifications and varieties

When heated, albite transforms from 980 ° C into its monoclinic high-temperature modifications .

Pericline from Moar Alp , Habachtal , Hohe Tauern, Salzburg, Austria (size: 23.5 × 14.9 × 6.4 cm)

Several varieties of the albite are known:

  • As periklin ( Greek : περίκλινής [periklinis], inclining all around), Breithaupt designated a milky white albite formed with platy crystals in 1823
  • Cleavelandite is an albite that occurs in thin-leaved tablets.
  • The mixed crystal oligoclase with an albite content of 90 to 70% (about 10-30%) is assigned as a variety to the albite. It is best known for its sub-variety sunstone , which is reddish-brown in color and has a strong glitter due to the many embedded hematite scales. Under the trade name Canadian moonstone (also peristerite ), an oligoclase variety similar to moonstone is also known.

Education and Locations

Large albite crystal (white) with muscovite (brownish) and beryl (light blue) from the Shigar Valley, Pakistan (size: 7.5 × 4.4 × 4.0 cm)
Albite (white) with Schörl (black tourmaline ) and Spessartine (orange) from the "Little Three Mine", Ramona (California) (size: 5.7 × 5 × 2.5 cm)

Albite forms either magmatically in granites , metamorphically in orthogneiss and phyllites or hydrothermally in veins. In addition to its mixed crystal and group partners, albite can also occur with many different minerals in Paragenesis , including biotite , fluorite , muscovite , quartz and various tourmalines, as well as ore minerals such as spodumene , amblygonite , cassiterite and tantalite (Mn) .

As a frequent mineral formation, albite can be found in many localities, whereby so far (as of 2013) around 8000 localities are known. In addition to its type locality, the "Finnbo" quarry near Falun, the mineral occurred in Sweden, among others, near Älvdalen , Hedemora and on Öster Silvberg in the municipality of Säter in Dalarna; near Berghamn in Ångermanland ; at Jokkmokk , Kiruna and Storuman in Lapland; at Båraryd and Jönköping in Småland; at Filipstad in Värmland and at Lindesberg , Nora and Sala in Västmanland.

Amelia County in Virginia and District Pala ( San Diego County ) in California in the USA, where well-developed cleaveland crystals with a diameter of up to 15 cm were found in pegmatite cavities, are known for their extraordinary albite finds.

In Germany the mineral could so far mainly in many places in the Black Forest in Baden-Württemberg; in the Fichtel Mountains , the Swabian-Franconian Forest Mountains , in the Bavarian Forest and the Upper Palatinate Forest in Bavaria; in some places in the Hessian Odenwald ; in many places in the Harz Mountains from Lower Saxony to Saxony-Anhalt; near Stolberg , Winterberg and in the Siebengebirge near Bonn and Königswinter in North Rhine-Westphalia; in many places in the Eifel (Mendig, Ettringen, Remagen) in Rhineland-Palatinate; on Petersberg near Halle in Saxony-Anhalt; can be found in many places in the Saxon Ore Mountains as well as near Ronneburg , Schnellbach (Floh-Seligenthal) and Weitisberga in Thuringia.

In Austria, albite was found in the Friesach - Hüttenberg area , the Ankogel and Goldberg groups, and in the Koralpe and Saualpe in Carinthia; in the Lower Austrian regions of Wachau and Waldviertel ; in Gastein , Habachtal , Raurisertal and Untersulzbachtal and Salzburg; in the Fischbacher Alps , the Koralpe and in the districts of Leoben and Weiz in Styria; in the Kalser Tal , Tauerntal and Zillertal in Tyrol; in the Mühlviertel in Upper Austria and in the Verwall Group in Vorarlberg.

In Switzerland, the mineral is mainly known from the cantons of Graubünden (Calanda, Domleschg, Engadin, Medeltal), Ticino (Valle Leventina, Valle Maggia) and Uri (Maderanertal, Reuss valley), Wallis (Binntal, Oberwald, Val d'Anniviers, Zermatt).

Other locations include Afghanistan, Egypt, Algeria, Angola, the Antarctic, Argentina, Armenia, Australia, Belgium, Bolivia, Brazil, Bulgaria, Chile, China, Finland, France, Canada, Colombia, Myanmar, Czech Republic, Greece, Greenland, Hungary, India, Indonesia, Iran, Ireland, Italy, Japan, Kazakhstan, Kyrgyzstan, Korea, Madagascar, Malawi, Morocco, Mexico, Mongolia, Mozambique, Namibia, Nepal, New Zealand, Nigeria, Norway, Oman, in Pakistan, Paraguay, Peru, Poland, Portugal, Rwanda, Romania, Russia, Zambia, Saudi Arabia, Zimbabwe, Slovakia, Slovenia, Spain, South Africa, Sudan, Tajikistan, Tanzania, Turkey, Ukraine, Uzbekistan, im United Kingdom (UK) and the United States of America (USA).

Also in mineral samples from the Mid-Atlantic Ridge (hydrothermal field “Logatchev-1”, “Markov Depth”), from the Central Indian Ridge (MESO Mineral Zone, “Site 253” 90 ° East) and from the East Pacific Ridge (ultramafic complex “Hess Depth”) as well outside the earth on the moon ( Rima Hadley ) albite could be detected.

use

Due to its low alkali content, albite is of secondary importance for the ceramic industry. Only its varieties oligoclase or sunstone and Canadian moonstone are occasionally used as gem stones , whereby these are usually imitated by synthetic gold flux or white labradorite due to their rarity .

See also

literature

Web links

Commons : Albite  - collection of images, videos and audio files
Wiktionary: Albit  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ a b c Helmut Schrätze, Karl-Ludwig Weiner: Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 881 .
  2. ↑ Webmineral - Albite (English)
  3. ↑ 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.
  4. ↑ a b c Mindat - Albite (English)
  5. ↑ a b Albite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 84.3 kB )
  6. ^ Helmut Schrätze, Karl-Ludwig Weiner: Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 861 .
  7. ^ A b Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  695 .
  8. ↑ OF Tuttle, NL Bowen (1950): High-temperature albite and contiguous field spars. J. Geol. 58 (5), 572-583, http://www.jstor.org/stable/30068571
  9. ^ A b Helmut Schrätze, Karl-Ludwig Weiner: Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 882 .
  10. ^ Mineral Atlas: Albite
  11. ^ Helmut Schrätze, Karl-Ludwig Weiner: Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 885-886 .
  12. ↑ Hans Lüschen: The names of the stones. The mineral kingdom in the mirror of language . 2nd Edition. Ott Verlag, Thun 1979, ISBN 3-7225-6265-1 , p. 167 .
  13. ↑ Ulrich Henn: Gemstone Dictionary . Ed .: German Gemmological Society. Self-published, Idar-Oberstein 2001, ISBN 3-932515-24-2 , p. 49 .
  14. ^ Institute for Gem Testing (EPI) - Search for Canadian Moonstone ( Memento from July 27, 2013 in the Internet Archive )
  15. ↑ Mindat - Number of localities for Albite
  16. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 265 ( Dörfler Natur ).
  17. ↑ a b List of locations for albite in the Mineralienatlas and Mindat