Lawsonite

Lawsonite is a rarely occurring mineral from the mineral class of silicates and the order of the group silicates ( Sorosilikate ) with the chemical composition CaAl2 [( OH) 2 | Si2O7 ] • H2O. By substituting only a small fraction can be replaced Al3 by Fe2 / 3 , Ti4 , Mg2 and Ca2 by Na .

Lawsonite crystallized in the orthorhombic crystal system and usually develops tabular or short prismatic crystals can be colored either colorless or white, blue green or blue-gray.

Etymology and history

Lawsonite was named after the Scottish- American geologist Andrew Cowper Lawson ( 1861-1952 ).

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the lawsonite belonged to the mineral class of " silicates and Germanates " and then to the Department of " group silicates ( Sorosilikate ) ", where he held a along with Hennomartinit, ilvaite, Itoigawait and Noelbensonit independent group was formed.

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the lawsonite also included in the category of " silicates and Germanates " and there in the department of " group silicates ( Sorosilikate ) ". This division, however, is further subdivided according to the nature and linkage of the silicate groups and the coordination of the cations involved, so that the mineral according to its crystal structure in the subdivision " Si2O7 groups with additional anions; Cations " is to find where it is named as the " in octahedral coordination and greater Lawsonitgruppe "with the system no. Forms 9.BE.05 and the other members Hennomartinit, Itoigawait and Noelbensonit.

The mainly common in English-speaking classification of minerals according to Dana assigns the lawsonite in the class of " silicates and Germanates " there, however, in the already fine divided department of " group silicates: Si2O7 Groups and O, OH, F, and H2O" a. Here he is with ilvaite namesake of the " lawsonite - ilvaite group " with the system no. 56.02.03 and the other members Hennomartinit, Itoigawait, Noelbensonit and Manganilvait within the sub-division of " group silicates: Si2O7 Groups and O, OH, F, and H 2 O with cations in and / or > coordination ".

Education and Locations

Lawsonite is a typical mineral of the blueschist metamorphism (high pressure - low temperature ) and comes from the transformation of basaltic and gabbroic rocks. Therefore, one finds lawsonite mainly in collisional orogens.

Locations include Port Macquarie in Australia, the Alps in Germany, the Apennines and Corsica in Italy, Briançon in France, Salzburg in Austria and the province of Villa Clara in Cuba.

Morphology

Most lawsonite is formed by tabular { 010 }, rarely slightly stretched as squat prism. Often lawsonite is also available xenomorph and as a granular aggregate.

Crystal structure

Lawsonite crystallized in the orthorhombic space group Cmcm ( Raumgruppen-Nr. 63) with the lattice parameters a = 5.85 Å; b = 8.79 Å and c = 13.13 Å and four formula units per unit cell.