Augelith

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Augelith
Augelite-78933.jpg
Augelith crystal group from the Peruvian region of Ancash (size: 4 cm × 4 × 2 cm)
General and classification
chemical formula Al 2 [(OH) 3 | PO 4 ]
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.BE.05 ( 8th edition : VII / B.12)
06/41/08/01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group C 2 / m (No. 12)Template: room group / 12
Lattice parameters a  = 13.12  Å ; b  = 7.99 Å; c  = 5.07 Å
β  = 112.2 °
Formula units Z  = 4
Frequent crystal faces {110}, {001}, { 2 01}, { 1 11}
Physical Properties
Mohs hardness 4.5 to 5
Density (g / cm 3 ) measured: 2.696; calculated: 2.704
Cleavage perfect after {110}, imperfect after {001} and { 1 01}, good after { 2 01}
Break ; Tenacity uneven; brittle
colour colorless, white, light pink, yellowish, greenish, rarely also bluish
Line color White
transparency transparent to translucent
shine Glass luster, pearlescent luster on cleavage surfaces
Crystal optics
Refractive indices n α  = 1.574
n β  = 1.576
n γ  = 1.588
Birefringence δ = 0.014
Optical character biaxial positive
Axis angle 2V = 51 ° (measured); 48 ° (calculated)

Augelith (not to be confused with the similarly named Augite ) is a rarely occurring mineral from the mineral class of " phosphates , arsenates and vanadates " with the chemical composition Al 2 [(OH) 3 | PO 4 ] and is therefore chemically an aluminum - Phosphate with additional hydroxide ions .

Augelith crystallizes in the monoclinic crystal system and develops mostly flat, thick tabular or needle-like to prismatic crystals up to 13 centimeters in size, but also occurs in the form of granular to massive mineral aggregates . In its pure form it is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline training, it can also appear white and, due to foreign admixtures, take on a light pink, yellowish or greenish and rarely also bluish color, whereby its transparency decreases accordingly. Unharmed crystal surfaces have a glass-like sheen , whereas cleavage surfaces have a mother-of-pearl shimmer.

With a Mohs hardness of 4.5 to 5, Augelith is one of the medium-hard minerals, which roughly corresponds to the hardness of rhinestones . Similar to the reference minerals fluorite (4) and apatite (5), it can be scratched with a knife.

Etymology and history

Augelith was first discovered in the “Västanå” iron mine near Näsum in the Swedish municipality of Bromölla and described in 1868 by Christian Wilhelm Blomstrand , who named the mineral after the Greek words αὐγή auge , which means something like shine, and λίθος lithos for “stone “Named; put together "shiny stone".

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the Augelith belonged to the department of "Anhydrous phosphates, with foreign anions F, Cl, O, OH", where together with Brasilianit and Viitaniemiit it belonged to the unnamed group VII / B .12 made.

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns the Augelith to the category of “Phosphates etc. with additional anions; without H 2 O “. However, this is further subdivided according to the relative size of the cations involved and the molar ratio of the additional anions (OH etc.) to the phosphate, arsenate or vanadate complex (RO 4 ), so that the mineral can be classified in the sub-section " With only medium-sized cations; (OH etc.): RO 4  > 2: 1 “can be found where it is the only member of the unnamed group 8.BE.05 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Augelith to the class of "phosphates, arsenates and vanadates" and there in the department of "anhydrous phosphates etc., with hydroxyl or halogen". Here he is the only member of the unnamed group 06/41/08 within the sub-section “Anhydrous phosphates etc., with hydroxyl or halogen with (A) 2 (XO 4 ) Z q ”.

Crystal structure

Augelith crystallizes monoclinically in the space group C 2 / m (space group no. 12) with the lattice parameters a  = 13.12  Å ; b  = 7.99 Å; c  = 5.07 Å and β = 112.2 ° as well as 4 formula units per unit cell . Template: room group / 12

Education and Locations

Yellowish Augelith from Dawson (Yukon) , Canada (size: 2.6 cm)
Augelith (white) on siderite (greenish brown) from the "Tazna Mine", Cerro Tazna , Nor Chichas Province , Bolivia (size: 9.0 × 6.5 × 1.9 cm)

Augelith is secondary to hydrothermal processes in granitic pegmatites as a substitute product from primary phosphates. It is seldom metamorphic in quartzites . Accompanying minerals include andorite , arsenopyrite , attacolite , barite , berlinite , hematite , cassiterite , lazulite , pyrite , pyrophyllite , rutile , stannite , svanbergite , trolleite and zincite .

As a rare mineral formation, Augelith could only be detected at a few sites, whereby so far (as of 2013) around 70 sites are known. In addition to its type locality "Västanå" near Näsum in Skåne län, the mineral was found in Sweden near Norrskogen in Uppland , at the Hålsjöberg quarry (Horrsjöberg) near Torsby and at Hökensås near Tidaholm in Västergötland.

The Burango pegmatites in the district of Gatumba in the western province of Rwanda, where massive aggregates several decimetres in size emerged, are known due to the extraordinary finds of eyelite .

In Austria, Augelith was found at Lake Millstatt and near Wolfsberg in Carinthia, as well as at Freßnitzgraben , Pretulgraben / Langenwang and near Hönigsberg in Styria.

Other sites are among others in Australia, Bolivia, Brazil, China, Finland, France, Japan, Canada, Madagascar, Mexico, Peru, Russia, Senegal, Spain, Czech Republic, Uganda as well as various sites in several states of the USA.

use

Augelith often forms beautiful and shiny crystal steps, the clear crystals of which are partly also gem quality. However, due to its good cleavability and relatively low hardness, it is too sensitive for commercial use. Nevertheless, it is occasionally offered to collectors in various shapes .

See also

literature

  • CW Blomstrand : Om Westanå mineralier . In: Öfversigt af Kongliga Vetenskaps-Akademiens Förhandlingar . tape 25 , 1868, p. 197–212 (Swedish, rruff.info [PDF; 933 kB ; accessed on August 5, 2017]).
  • GT Prior, LJ Spencer: Augelite . In: Mineralogical Magazine . tape 11 , 1895, p. 16–23 (English, rruff.info [PDF; 316 kB ; accessed on August 5, 2017]).
  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 630–631 (first edition: 1891).

Web links

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

Individual evidence

  1. ↑ 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.  449 .
  2. ↑ a b c d e f Augelite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 66  kB ; accessed on August 5, 2017]).
  3. ↑ a b c d e Mindat - Augelite
  4. ↑ Mindat - Number of localities for Augelith
  5. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Dörfler Natur ). Nebel Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 164 .
  6. ↑ Find location list for Augelith in the Mineralienatlas and in [Mindat]
  7. ^ 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. 226 .