Agrellite

• IMA 1973-032

The mineral Agrellit is a very rarely occurring chain silicate mineral from the class of " silicate and germanate ". It crystallizes in the triclinic crystal system with the chemical composition NaCa2 [ F | Si4O10 ] and usually develops long-prismatic crystals up to about 10 cm in length, but also tabular mineral aggregates of grayish white to greenish color.

Special Features

Agrellit shows under long-wave UV light, bright purple and under short-wave UV light, a dark violet fluorescence.

Etymology and history

Was first found in Kipawa 1973 Agrellit complex of Témiscamingue in Canada and described in 1976 by ​​J. Gittins, MG Brown and B.D. Sturman, who named the mineral after the English mineralogist Dr. Stuart Olof Agrell ( 1913-1996 ).

Classification

In the now outdated 8th edition of the mineral classification by Strunz the Agrellit still belongs to the department of " layer silicates ( phyllosilicates ) ," where he formed his own group together with Glagolevit and Mountainit.

Since the revision of the Strunz'schen Mineral classification in the 9th edition, however, the mineral is re- sorted into the sub-division of " chains and chain silicates with 4- periodic single chains, Si4O12 ," where it is the only member of the unnamed group 9.DH.75 forms.

The commonly used in English-speaking classification of minerals according to Dana sorted the Agrellit also in the Department of Kettensilicate, there, however, in the subdivision " with column or tube structures with columnar silicate units ," where he along with Litidionit, Fenaksit and Manaksit the unnamed group 70.1.1 forms.

Education and Locations

Agrellit metamorphic forms in alkaline gneisses.

Apart from its type locality Kipawa complex in Canada, the mineral world was still at about 10 localities (as of 2010) are detected, including in Moron - massif of Aldanhochlandes ( Eastern Siberia ) and the Chibinen on the Kola Peninsula in Russia; the Darai - Pioz glacier in Alay Mountains of Tajikistan, as well as in Wausau plateau and in the plutons near Stettin (Wisconsin ) in the USA.

Crystal structure

Agrellit crystallizes in the triclinic space group P1 with the lattice parameters a = 7.76 Å; b = 18.95 Å; c = 6.99 Å; α = 89.9 °; β = 116.6 ° and γ = 94.3 °, and four formula units per unit cell.