Clinozoisite

Clinozoisite is a mineral from the mineral class of " silicates and Germanates ". Due to the close chemical relationship to epidote within the group it belongs to the silicates Epidotgruppe. It crystallizes in the monoclinic crystal system with the chemical composition Ca2AlAl2 [O | OH | SiO4 | Si2O7 ] and developed fibrous to long prismatic, partly kurzsäulige crystals.

Special Features

The distinction between clinozoisite and very similar Epidots (Ca2 ( Fe3 , Al) Al 2 [O | OH | SiO4 | Si2O7 ] ) via the optical properties in thin section under the polarizing microscope. Klinozoisit virtue of the absence of Fe3 ions lower refractive indices than epidote, continues its optical orientation is biaxial positive as opposed to negative biaxial epidote. From chemically identical, orthorhombic zoisite it can be distinguished by the oblique extinction.

Etymology and history

First described scientifically and is recognized as a separate mineral was Klinozoisit by Ernst Weinschenk ( 1865-1921 ). The contract awarded by him name means as much as " the crooked zoisite " and is based on the close relationship to the chemically identical but orthorhombic zoisite, clinozoisite while in the monoclinic crystal system crystallizes.

Classification

In the now outdated nomenclature of minerals by Strunz ( 8th edition ) of clinozoisite still belongs to the general ward of the "Group silicates ( Sorosilikate ) ", where he is a member of the large group of epidote.

Since the revision of the Strunz'schen Mineral classification in its 9th edition, this department is precisely divided 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 SiO4 and Si2O7 groups; Cations in oktahedraler and greater coordination " and there is still a member of the Epidotgruppe with the system no. 9.BG.05.

The commonly used in English-speaking classification of minerals according to Dana assigns the clinozoisite also in the department of the group silicates, there, however, in the subdivision of " group silicates with insular, mixed, individual and larger groups with cations in tetrahedral and higher coordination; Single and double groups (n = 1,2). " Again, he is a member of Epidotgruppe, specifically the " epidote - subgroup ".

Education and Locations

Clinozoisite occurs primarily in the metamorphism and is typical of the rocks of greenschist and amphibolite facies. Secondary to Klinozoisit also forms by the hydrothermal alteration of plagioclase in igneous rocks. Accompanying minerals ( mineral assemblages ) are often epidote, chlorite different, prehnite, albite, quartz and calcite, rarely, biotite, stilpnomelane, pumpellyite, and various grenade.

Clinozoisite is colorless, however, by Fe3 ions in the squares of Al3 in the crystal structure pale yellow to green, by Mn2 in the squares of Ca2 weakly reddish to pink (rarely ) be colored.

Known localities are located in Switzerland, Austria, Mexico, California, Madagascar and New Zealand's Southern Alps.

Crystal structure

Klinozosit crystallizes in the monoclinic space group ( Raumgruppen-Nr. 11) with the lattice parameters a = 8.88 Å; b = 5.58 Å; c = 10.15 Å and β = & nbsp115, 2 ° and two formula units per unit cell.

The chemical structure consists of mixed island [ SiO4 ] and disilicates [ Si2O7 ] with3 (OH )