Clinozoisite
| Clinozoisite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | Ca 2 AlAl 2 [O | OH | SiO 4 | Si 2 O 7 ] |
|
Mineral class (and possibly department) |
Silicates and Germanates |
|
System no. to Strunz and to Dana |
9.BG.05 ( 8th edition : VIII / C.23) 58.02.01a.01 |
| Similar minerals | Epidote , zoisite, piedmontite , allanite |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic 2 / m |
| Room group (no.) | P 2 1 m (No. 11) |
| Lattice parameters |
a = 8.88 Å ; b = 5.58 Å; c = 10.15 Å β = 115.2 ° |
| Formula units | Z = 2 |
| Frequent crystal faces | {100}, {111}, {001} |
| Twinning | lamellar after {100}, rare |
| Physical Properties | |
| Mohs hardness | 6.5 to 7 |
| Density (g / cm 3 ) | 3.21 to 3.38 |
| Cleavage | {001} perfect |
| Break ; Tenacity | uneven |
| colour | colorless, e.g. T. pale yellow, gray, green; colorless in thin section |
| Line color | grayish, white |
| transparency | transparent to translucent |
| shine | Glass gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.670 to 1.718 n β = 1.670 to 1.725 n γ = 1.690 to 1.734 |
| Birefringence | δ = 0.004 to 0.015 |
| Optical character | biaxial positive |
| Axis angle | 2V = 14 to 90 ° |
| Pleochroism | not available, with small amounts of Fe 3+ slightly yellow to green |
| Other properties | |
| Chemical behavior | insoluble in water and hydrochloric acid |
Clinozoisite is a mineral from the mineral class of " silicates and germanates ". Due to the close chemical relationship to epidote , it belongs to the epidote group within the group silicates . It crystallizes in the monoclinic crystal system with the chemical composition Ca 2 AlAl 2 [O | OH | SiO 4 | Si 2 O 7 ] and develops fibrous to long prismatic, sometimes also short columnar crystals .
Special properties
The distinction between clinozoisite and the very similar epidote (Ca 2 (Fe 3+ , Al) Al 2 [O | OH | SiO 4 | Si 2 O 7 ]) is based on the optical properties in the thin section under the polarizing microscope . Due to the lack of Fe 3+ ions, clinozoisite has lower refractive indices than epidote, and its optical orientation is biaxially positive in contrast to the biaxially negative epidote. It can be distinguished from the chemically identical, orthorhombic zoisite by the oblique extinction .
Etymology and history
Clinozoisite was first scientifically described and recognized as an independent mineral by Ernst Weinschenk (1865–1921). The name given by him means something like "the crooked zoisite" and is based on the close relationship to the chemically identical, but orthorhombic zoisite, while clinozoisite crystallizes in the monoclinic crystal system.
classification
In the meanwhile outdated system of minerals according to Strunz (8th edition) the clinozoisite still belongs to the general department of " group silicates (sorosilicates)", where it is a member of the large group of epidotes .
Since the revision of Strunz's mineral classification in the 9th edition , this section has been subdivided more precisely according to the type of silicate complexes occurring in the compound and the coordination of the cations involved . The clinozoisite is accordingly in the subdivision of “Group silicates with mixed SiO 4 and Si 2 O 7 groups; Cations in octahedral [6] and greater coordination ”and is still a member of the epidote group with the system no. 9.BG.05 .
The systematics of minerals according to Dana , which is common in the English-speaking area , also assigns the clinozoisite to the group of silicates, but there in the subdivision of "group silicates with insular, mixed, individual and larger tetrahedral groups with cations in [6] and higher coordination; Single and double groups (n = 1.2) ”. Here, too, he is a member of the epidote group , more precisely the "epidote subgroup".
Education and Locations
Clinozoisite occurs primarily during rock metamorphosis and is typical of the rocks of green schist and amphibolite facies. Secondarily, clinozoisite is also formed by the hydrothermal alteration of plagioclase in igneous rocks . Accompanying minerals ( paragenesis ) are often epidote, various chlorites , prehnite , albite , quartz and calcite , more rarely also biotite , stilpnomelane , pumpellyite and various garnets .
Clinozoisite is colorless, but can be colored pale yellow to green due to Fe 3+ ions in the places of Al 3+ in the crystal structure, and slightly reddish to pink (rarely) due to Mn 2+ in the places of Ca 2+ .
Well-known sites are in Switzerland , Austria , Mexico , California , Madagascar and the New Zealand Alps .
Crystal structure
Klinozosit crystallizes monoclinically in the space group (space group no. 11) with the lattice parameters a = 8.88 Å ; b = 5.58 Å; c = 10.15 Å and β = 115.2 ° and 2 formula units per unit cell .
The chemical structure consists of mixed island [SiO 4 ] and disilicates [Si 2 O 7 ] with 3 (OH)
See also
Individual evidence
- ↑ a b c d e 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. 585 .
literature
- P. Comodi, PF Zanazzi: The pressure behavior of clionzoisite and zoisite: An x-ray diffraction study . In: American Mineralogist . Vol. 82, 1997, pp. 61-68. (English)
- WA Deer, RA Howie, J. Zussman: An Introduction to the Rock Forming Minerals . Prentice Hall, Harlow 1992, ISBN 0-582-30094-0 (English)
Web links
- Clinozoisite data on webmineral.com (English)
- Mineral Atlas: Clinozoisite (Wiki)