Albite
- Sodium feldspar
Albite or sodium feldspar is a very common mineral from the mineral class of " silicates and Germanates ". It crystallizes in the triclinic crystal system having the idealized chemical composition Na [ AlSi3O8 ], is provided as a sodium aluminum silicate. Structurally, it belongs to the framework silicates ( tectosilicates ).
Albite belongs to the large family of feldspars, where it forms the sodium- rich end member of the solid solution and the ternary system Orthoclase (K [ AlSi3O8 ] ) - albite - anorthite (Ca [ Al2Si2O8 ] ) in the group of plagioclase with the intermediate members oligoclase, andesine, labradorite and Bytownite. Due to the formation of mixed crystals the formula for sodium- rich plagioclase feldspars are generally denoted with (Na, Ca) [ (Si, Al) 4O8 ]. Since one can not distinguish macroscopically the mixed crystals, these were arbitrarily divided according to increasing anorthite, albite which can contain up to 10% anorthite in order to be designated as such must.
Albite developed mainly rich surface, tabular to prismatic crystals and twins, with polysynthetic twins are usually recognizable by their striped crystal faces. Also known are granular to massive mineral aggregates. In its pure form albite is colorless and transparent. But it may also appear white and accept by foreign admixtures a gray, yellowish, reddish, greenish or bluish color through multiple light refraction due to lattice defects or polycrystalline training, the transparency decreases accordingly. Clear and uninjured crystal faces have a glass-like luster, cleavage surfaces shimmer contrast nacreous.
Etymology and history
Albite was first scientifically described in 1815 by Johan Gottlieb Gahn notified and Jöns Jakob Berzelius, which due to its predominantly white color after the Latin word albus for "knows" the mineral.
As a type locality of quartz and pegmatite quarry " Finnbo " applies in Falun in the Swedish province of Dalarna County.
Classification
Already in the outdated, but partly still in use 8th edition of the mineral classification by Strunz belonged albite to the mineral class of " silicates and Germanates " and there to the general ward of the " framework silicates ( tectosilicates ) " where he as a member of the subgroup of " plagioclase "with the system number. VIII/J.07 can be found within the feldspar.
The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns albite in the fine already divided the department " framework silicates ( tectosilicates ) without zeolitic H2O" one. This is further subdivided according to the possible presence of additional anions, so that the mineral is found according to its composition in the subsection " framework silicates ( tectosilicates ) without additional anions ", where it together with anorthite, the intermediate pontics andesine, Bytownite, labradorite and oligoclase the subset of the " plagioclase " with the system number. 9.FA.35 forms. Also included in this group, the mineral is Reedmergnerit.
The classification of minerals according to Dana assigns albite in the class of " silicates and Germanates " and there in the department of " framework silicates: Al- Si lattice ". He is also in the " plagioclase series" with the system no. 76.01.03 found within the subdivision " with ( simple ) Al- Si lattice ".
Modifications and varieties
When heated, albite transforms into his monoclinic high-temperature modifications from 980 ° C.
From albite several varieties are known:
- As Pericline (Greek: περίκλινής [ periklinos ], located around tending ) designated Breithaupt 1823 a milky white, trained with platy crystals albite
- Cleavelandit is occurring in thin-leaf tablets albite.
- The mixed crystal oligoclase is associated with a Albitgehalt 90-70 % ( to 10-30 %) than the variety albite. He is known primarily for his subvariety Sunstone, which is colored reddish brown because of many of stored Hämatitschüppchen and strong glitters. Under the trade name of Canadian Moonstone (also Peristerit ) is also one of the moonstone similar oligoclase - known variety.
Education and Locations
Albite forms either magmatic granites, metamorphic, among other ortho gneisses and phyllites or hydrothermally in veins. Albite paragenesis can in addition to its solid solution and group partners still occur with many different minerals, so among other things, biotite, fluorite, muscovite, quartz and various tourmalines.
As a frequent mineral formation albite is found in many localities, where so far (as of 2013) are considered to be known around 8000 localities. Apart from its type locality, the quarry " Finnbo " Falun mineral occurred in Sweden, among others, still in Älvdalen, Hedemora and Austria on Silvberg in the town Sater in Dalarna; at Berghamn in Ångermanland; in Jokkmokk, Kiruna and Storuman in Lapland; at Båraryd and Jönköping in Småland; at Filipstad in Värmland and in Lindenberg, Nora and Sala in Västmanland on.
Known due to exceptional Albitfunde include the Amelia County, Virginia and the District Pala (San Diego County) in California in the United States, where in pegmatite cavities well-developed Cleavelandkristalle of up to 15 cm in diameter were revealed.
In Germany, the mineral has been able especially in many places in the Black Forest in Baden- Württemberg; in the Fichtelgebirge, the Swabian-Franconian Forest mountains, in the Bavarian Forest, 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; at Stolberg, Winterberg and in the Seven Mountains near Bonn and King Winter in North Rhine -Westphalia; in many places in the Eifel ( Mendig, Ettringen, Remagen ) in Rhineland -Palatinate; at the Petersberg near Halle in Saxony -Anhalt; in many places in the Saxon Erzgebirge and in Ronneburg, Schnellbach ( flea Seligenthal ) and Weitisberga in Thuringia be found.
In Austria they found albite, among others in the area Friesach - hut mountain, the Ankogel and the Goldenberg Group and in the Kor and Saualpe in Carinthia; in the Lower Austrian Waldviertel Wachau Valley and regions; in the Gastein Valley, Habachtal, Raurisertal and Untersulzbachtal and Salzburg; in the Fischbacher Alps, the Kor, and in the districts of Leoben and Weiz in Styria; in the Kals Valley, Zillertal in Tyrol and Tauerntal; in Upper Austria Upper Austria as well as in the Verwallgruppe in Vorarlberg.
In Switzerland, you know the mineral mainly from the cantons of Graubünden ( Calanda, Domleschg, Engadine, Medeltal ), Ticino ( Leventina Valley, Valle Maggia ) and Uri ( Maderan Reusstal ), Wallis ( Binn Valley, Upper Forest, Val d' Anniviers, Zermatt )
Other localities lie include Afghanistan, Algeria, Angola, Antarctica, 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, Pakistan, Paraguay, Peru, Poland, Portugal, Rwanda, Romania, Russia, Zambia, Saudi Arabia, Zimbabwe, Slovakia, Slovenia, Spain, South Africa, Sudan, Tajikistan, Tanzania, Turkey, Ukraine, Uzbekistan, in 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 the East Pacific Rise ( ultramafic complex " Hess- depth ") and outside the Earth to the Moon ( Rima Hadley ) could be detected albite.
Morphology
Albite is predominantly in the form of lamellar crystal twins twins from repetition, which is manifested by their characteristic striations on the crystal faces. Preference is given to two twin laws, one of which was named after the albite.
In the " albite - law" is the b- surface (010 ), the intergrowth of the twins. To the base results in a re-entrant angle of 7 ° 12 ' and 8 ° 20'. The " gap area " c, but also all other surfaces ( with the exception of b) are longitudinally striped by lamellar repeat this Act. Due to the characteristic of all plagioclase Zwillingsstreifung, these relatively easy to distinguish in the rock of the Kalifeldspaten. Visible but these are usually only under the microscope.
When " pericline law" is the twin axis parallel to the b axis. The Verwachsungsfläche here is either the base, with cover over the twin halves or the so-called " X-Plane " or the " rhombic section " in which successive fit both twin halves. The " rhomboidal section " is changed depending on the composition of the plagioclase its position relative to the crystallographic axes, and can therefore be used for the optical determination.
Crystal structure
From albite two structural modifications are known, both crystallize in the triclinic crystal system in space group C1 ( Raumgruppen-Nr. 2) with slightly different lattice parameters. The lattice parameters are in four formula units per unit cell for
- High - albite: a = 8.16 Å; b = 12.88 Å; c = 7.11 Å; α = 93.5 °; β = 116.5 ° and γ = 90.2 °
- Low - albite: a = 8.14 Å; b = 12.79 Å; c = 7.16 Å; α = 94.2 °; β = 116.6 ° and γ = 87.7 °
Use
Albite is only of minor importance due to its low alkali content for the ceramic industry. Only the varieties or oligoclase sunstone and moonstone Canadian occasionally find use as a gemstone, which are imitated because of their rarity mostly by synthetic gold river or white labradorite.