Amstallite

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Amstallite
General and classification
other names

IMA 1986-030

chemical formula CaAl 2 Si 3 O 8 (OH) 4  H 2 O (idealized)

CaAl (OH) 2 [Al 0.8 Si 3.2 O 8 ] [(H 2 O) 0.8 Cl 0.2 ] (empirically determined)

Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.DP.25 ( 8th edition : VIII / G.07)
72.01.04.01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic 2 / m
Room group (no.) C 2 / c (No. 15)
Lattice parameters a  = 18.83  Å ; b  = 11.52 Å; c  = 5.19 Å
β  = 100.9 °
Formula units Z  = 4
Physical Properties
Mohs hardness 4th
Density (g / cm 3 ) measured: 2.40 (5); calculated: 2.38
Cleavage good after {100}
Break ; Tenacity clamshell; brittle
colour colorless
Line color White
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.533
n β  = 1.534
n γ  = 1.538
Birefringence δ = 0.005
Optical character biaxial positive
Axis angle 2V = 57 to 59 ° (measured); 54 ° (calculated)

The mineral amstallite is a very rarely occurring chain silicate from the mineral class of " silicates and germanates ". It crystallizes in the monoclinic crystal system with the idealized composition CaAl 2 Si 3 O 8 (OH) 4  · H 2 O or CaAl [(OH) 2 | AlSi 3 O 8 (OH) 2 ] · H 2 O ( crystal chemical structural formula ), is thus seen a chemically complex composition and water-containing calcium - aluminum silicate.

Amstallite develops colorless and transparent to translucent crystals with a needle-like to prismatic habit , which are generally stretched and streaked at right angles to the c-axis.

Etymology and history

Amstallite was first discovered near Amstall , more precisely in the Weinberger graphite mining area near Mühldorf in Lower Austria, and described in 1987 by R. Quint, who named the mineral after its type of locality .

Type material of the mineral can be found in the Institute for Mineralogy and Crystallography of the University of Vienna and in the Natural History Museum Vienna .

classification

Amstallite belonged to the mineral class of "silicates and germanates" and there to the department of "transition structures between chain and layered silicates", where it belonged together with bavenite , chiavennite , prehnite , to the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz . Rudenkoit and Tvedalit formed the independent group VIII / G.07 .

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 amstallite to the class of "silicates and germanates", but there in the department of "chain and band silicates (inosilicates) " a. This section is further subdivided according to the structure of the chains or bands, so that the mineral can be found according to its composition in the subdivision “Transitional structures chain and band silicates - sheet silicates”, where it is the only member of the unnamed group 9.DP.25 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the amstallite to the class of "silicates and germanates", but there in the department of "layered silicates: two-dimensional unlimited layers with rings other than six-membered". Here he can be found together with Rudenkoit in the unnamed group 72.01.04 within the sub-section “ Layered silicates: two-dimensional unlimited layers with rings other than six-membered: 4-membered rings ”.

Education and Locations

Amstallite forms in pegmatite streaks in graphite schist and is mostly found there in paragenesis with plagioclases and potash feldspar as well as quartz , apatite , rutile , siderite , albite , laumontite , calcite and / or vivianite .

So far (as of 2011) Amstallite could only be detected at its type locality Amstall in Austria.

Crystal structure

Amstallite crystallizes monoclinically in the space group C 2 / c (space group no. 15) with the lattice parameters a  = 18.83  Å ; b  = 11.52 Å; c  = 5.19 Å and β = 100.9 ° as well as 4 formula units per unit cell .

See also

Individual evidence

  1. ↑ a b c d e f Amstallite , in: American Mineralogist - NEW MINERAL NAMES , Volume 73, pages 1492-1499, 1988 (PDF 1.03 MB)
  2. ↑ Webmineral - Amstallite
  3. ^ A b c 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.  655 .
  4. ↑ John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols: Amstallite , in: Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 75.1 kB )
  5. ↑ a b c d Mindat - Amstallite
  6. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 5th completely revised and supplemented edition. Weise, Munich 2008, ISBN 978-3-921656-70-9 .

literature

  • R. Quint (1987): Description and crystal structure of amstallite, CaAl (OH) 2 [A 10.8 Si 3.2 O 8 (OH) 2 ] • [(H 2 O) 0.8 C 10.2 ], a new mineral from Amstall, Austria , in: New Yearbook for Mineralogy , Monthly Issues, Volume 6, pp. 253–262

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