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Andalusite crystals.jpg
General and classification
chemical formula Al 2 [O | SiO 4 ]
Mineral class
(and possibly department)
Island silicates (nesosilicates) with additional anions
System no. to Strunz
and to Dana
9.AF.10 ( 8th edition : VIII / B.02)
Similar minerals Disthene and sillimanite (with andalusite the three aluminosilicates)
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal; 2 / m  2 / m  2 / m
Space group Pbnm (No. 62, position 3)Template: room group / 62.3
Lattice parameters a  = 7.7980  Å ; b  = 7.9031 Å; c  = 5.5566 Å
Formula units Z  = 4
Frequent crystal faces {110}, {001}
Twinning rarely on {101}
Physical Properties
Mohs hardness 6.5 to 7.5
Density (g / cm 3 ) 3.13 to 3.16
Cleavage good after {110}
Break ; Tenacity brittle, splintery, uneven
colour red, pink, gray-brown, yellowish, dark green or greenish
Line color White
transparency transparent to opaque
shine Glass gloss to matt
Crystal optics
Refractive indices n α  = 1.629 to 1.640
n β  = 1.633 to 1.644
n γ  = 1.638 to 1.650
Birefringence δ = 0.009 to 0.010
Optical character biaxial negative
Axis angle 2V = measured: 48 ° to 68 °; calculated: 80 ° to 84 °
Pleochroism strong: X = pink, pale red or yellow; Y = Z = colorless, pale yellow or greenish
Other properties
Chemical behavior not decomposed by HF
Special features weak green to yellow-green fluorescence ; Conversion to sericite

The mineral andalusite is a frequently occurring island silicate from the group of aluminosilicates and has the chemical composition Al 2 [O | SiO 4 ]. Andalusite crystallizes in the orthorhombic crystal system and develops mostly prismatic crystals with a square cross-section, but also fibrous, granular or massive aggregates in varying colors such as red, pink, gray-brown, yellow or green. Its Mohs hardness is between 6.5 and 7.5, its density is around 3.2 g / cm³ and its line color is white.

Etymology and history

The mineral was first described in 1798 by Jean-Claude Delamétherie . It was named after its first site, which was later recognized as atypical - the Serranía de Ronda near Málaga in the Spanish province of Andalusia .


In the old (8th edition) and new systematics of minerals (9th edition) according to Strunz , andalusite belongs to the division of "island silicates with non-tetrahedral anions (Neso-subsilicates)". The new Strunz'sche mineral classification now subdivides here more precisely according to the position of the cations in the crystal, so that the mineral is now part of the subdivision of "island silicates with additional anions and cations in [4] -, [5] - and / or only [6 ] -Coordination "and forms a separate group with Kanonait .

The systematics of minerals according to Dana , which is common in the English-speaking world , assigns andalusite to the division of "Island silicates: SiO 4 groups and O, OH, F and H 2 O with cations in [4] and> [4] coordination" and there together with canonite and yoderite in the "Al 2 SiO 5 (andalusite subgroup)" .

Crystal structure

Andalusite crystallizes in the orthorhombic crystal system in the space group Pnnm with the lattice parameters a = 7.7980  Å , b = 7.9031 Å and c = 5.5566 Å as well as four formula units per unit cell .

Modifications and varieties


In addition to andalusite, kyanite (disthene), which is mainly formed at high pressures, and sillimanite as a high-temperature phase are further modifications of the aluminosilicate .

The main varieties are the gray-black chiastolite , which stands out for its black cross made up of graphite deposits and carbonaceous inclusions, and the viridin, which is green in color due to the inclusion of iron and manganese ions .

Chrysanthemum stone , on the other hand, is a flower-shaped to leaf-shaped mineral aggregate , whereby the light andalusite crystals are embedded in a dark (mostly black) matrix.

Education and Locations

Andalusite forms under low pressure through thermal metamorphosis in metamorphic rocks such as Hornfels . The mineral is also found in pegmatites , sometimes even as gem stones and occasionally as mineral soaps in river sediments. Accompanying minerals include kyanite , sillimanite , cordierite , corundum , garnets , tourmalines and various mica .

Frequent sites for andalusite include Bimbowrie in Australia , Morro do Chapeú / Bahia in Brazil , Darmstadt and Gefrees in the Fichtel Mountains in Germany and the Alpe Lisens near Sellrain in Austria .


Andalusite gemstone collection in facet cut

As a raw material

Andalusite is used in the manufacture of porcelain and in the production of refractory building materials and materials . In contrast to other natural raw materials such as B. kyanite and sillimanite , andalusite does not need any pre-firing before it can be used as a refractory material, as it only has a relatively low volume expansion of 3 to 5%.

As a gem

Transparent andalusites of gem quality are rarely found and are therefore correspondingly valuable. When choosing the cut, clear to strong pleochroism must be taken into account in order to achieve an optimal color result.

See also


  • Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 201 .
  • Walter Schumann: Precious stones and gemstones . 13th edition. BLV Verlags GmbH, Munich 2002, ISBN 3-405-16332-3 , p. 194 .
  • Andalusite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( [PDF; 71 kB ; accessed on July 24, 2017]).

Web links

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

Individual evidence

  1. a b c d Webmineral - Andalusite (English)
  2. a b c American Mineralogist Crystal Structure Database - Andalusite (English, 1979)
  3. a b c d e Mindat - Andalusite (English)
  4. Mineral Atlas: Chrysanthemum Stone
  5. Find location list for andalusite in the Mineralienatlas and Mindat
  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.  688 .
  7. Wolfgang Kollenberg (Ed.): Technical ceramics: Fundamentals, materials, process engineering. Vulkan-Verlag, Essen 2004, ISBN 3-8027-2927-7 , p. 489 limited preview in the Google book search