Island silicates

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Island silicate anion of the grossular: Representation of the atoms on the left (red: Si, blue: O) and the resulting silicate tetrahedron (right).

As island silicates (nesosilicates) is referred to silicates , the silicate anions from isolated SiO 4 - tetrahedrons exist, d. H. the SiO 4 tetrahedra are not connected to one another via Si-O-Si bonds.

This department of silicates includes the important rock-forming minerals of the garnet and olive group , zircon and the economically or petrologically important aluminosilicates andalusite , sillimanite , thistle , staurolite and topaz .

The simple structure of the SiO 4 complex anion does not result in any pronounced directional dependence of the properties of the island silicates. They are often cubic, tetragonal, trigonal, hexagonal or orthorhombic and usually form isometric crystals. The minerals in this division are mostly hard and have a high refractive index and a relatively high density .

classification

In Liebau's mineral classification, the island silicates, like the group silicates and ring silicates, belong to the silicates with dimensionality 0. The extent of the silicate anions is not unlimited in any direction (0 dimensions).

Strunz's classification arranges the island silicates division (9.A) according to the chemical environment of the cations in the structure and according to the occurrence and type of other anions.

9.AA island silicates without further anions; Cations in tetrahedral [4] coordination

9.AB island silicates without further anions; Cations in tetrahedral [4] and greater coordination

9.AC island silicates without further anions; Cations in octahedral [6] coordination

9.AD island silicates without further anions; Cations in octahedral [6] and usually greater coordination

9.AE island silicates with additional (O, OH, F, H2O); Cations in tetrahedral [4] and usually greater coordination

9.AF island silicates with additional anions; Cations in [4], [5] and / or only [6] coordination

9.AG island silicates with additional anions; Cations in mostly [6] and> [6] coordination

9.AH island silicates with CO3, SO4, PO4, etc.

9.AJ Island silicates with BO3 triangles and / or B [4], Be [4] tetrahedra, corner-dividing with SiO4

9. AK Uranyl island and sheet silicates with U: Si = 2: 1

Individual evidence

  1. ↑ a b Liebau 1982
  2. ↑ a b University of Tübingen: Systematics of Minerals - Nesosilicates (island silicates)
  3. ↑ a b c d e f g h i j k l Mineral class 9.A according to Strunz 9th edition
  4. ↑ a b c d e f g h i j k l Nickel-Strunz Silicates Classification (Version 10)
  5. ↑ a b c d e f g h i j k l Nickel-Strunz Classification - Nesosilicates 10th edition

Web links

literature

  • F. Liebau (1982): Classification of Silicates in: Reviews in Mineralogy Volume 5: Orthosilicates; Mineralogical Society of America