Lawsonite
| Lawsonite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | CaAl 2 [(OH) 2 | Si 2 O 7 ] • H 2 O |
|
Mineral class (and possibly department) |
Silicates and germanates - group silicates (sorosilicates) |
|
System no. to Strunz and to Dana |
9.BE.05 ( 8th edition : VIII / C.10) 56.02.03.01 |
| Similar minerals | Zoisite , clinozoisite |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-dipyramidal 2 / m 2 / m 2 / m |
| Room group (no.) | Cmcm (No. 63) |
| Lattice parameters | a = 5.85 Å ; b = 8.79 Å; c = 13.13 Å |
| Formula units | Z = 4 |
| Frequent crystal faces | {100}, {010}, {001}, {101} |
| Twinning | simple or lamellar parallel to {101} |
| Physical Properties | |
| Mohs hardness | 6th |
| Density (g / cm 3 ) | 3.05 to 3.12 |
| Cleavage | completely according to {001}, {010} |
| Break ; Tenacity | brittle |
| colour | colorless, white, blue-green, blue-gray |
| Line color | White |
| transparency | transparent to translucent |
| shine | Glass gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.665 n β = 1.672 to 1.676 n γ = 1.684 to 1.686 |
| Birefringence | δ = 0.019 to 0.021 |
| Optical character | X = c; Y = a; Z = b; biaxial positive |
| Axis angle | 2V = 76 to 87 ° |
| Pleochroism | colorless or blue-yellow-colorless |
Lawsonite is a rarely occurring minerals from the mineral class of silicates and the order of the group of silicates (Sorosilikate) with the chemical composition CaAl 2 [(OH) 2 | Si 2 O 7 ] • H 2 O. By substitution , only a small proportion of Al 3+ can be replaced by Fe 2 + / 3 + , Ti 4+ , Mg 2+ and Ca 2+ by Na + .
Lawsonite crystallizes in the orthorhombic crystal system and develops mostly tabular or short, prismatic crystals that can be either colorless or white, blue-green or blue-gray in color.
Etymology and history
Lawsonite was named after the Scottish-American geologist Andrew Cowper Lawson (1861–1952).
classification
In the meanwhile outdated, but still in use 8th edition of the mineral systematics according to Strunz , the lawsonite belonged to the mineral class of "silicates and germanates" and there to the department of " group silicates (sorosilicates)", where together with hennomartinite , ilvaite , itoigawaite and noelbene sonite it was one formed an independent group.
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns Lawsonite to the class of "silicates and germanates" and there in the department of "group silicates (sorosilicates)". This division, however, is further divided by the nature and linkage of silicate groups and the coordination of the involved cations , so that the mineral according to its crystal structure in the subsection "Si 2 O 7 groups with additional anions ; Cations in octahedral [6] and greater coordination ”can be found, where the“ Lawsonite group ”with the system no. 9.BE.05 and the other members hennomartinite, itoigawait and noelbensonite .
The systematics of minerals according to Dana , which is predominantly used in the English-speaking area , also assigns the Lawsonite to the class of "silicates and Germanates", but there in the more finely divided division of "group silicates: Si 2 O 7 groups and O, OH, F and H 2 O “a. Here, together with Ilvait, he is the namesake of the "Lawsonit-Ilvait Group" with the system no. 56.02.03 and the other members hennomartinite, itoigawaite, noelbensonite and manganilvaite within the subdivision of the " group silicates: Si 2 O 7 groups and O, OH, F and H 2 O with cations in [4] and / or> [4]" -Coordination ".
Education and Locations
Lawsonite is a typical mineral of the blue schist metamorphosis (high pressure-low temperature) and arises from the transformation of basaltic and gabbroid rocks . Therefore, Lawsonite is mainly found in collision 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 .
-G-EmpireTheWorldOfGems.jpg)
morphology
Lawsonite is mostly tabular after {010}, more rarely slightly elongated as a compact prism. Lawsonite is often also xenomorphic and as a granular aggregate.
Crystal structure
Lawsonite crystallizes orthorhombically in the space group Cmcm (space group no. 63) with the lattice parameters a = 5.85 Å ; b = 8.79 Å and c = 13.13 Å and 4 formula units per unit cell .
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. 574 .
literature
- Nesse WD (2002): Introduction to Mineralogy. Oxford University Press.
- M. Okrusch, S, Matthes: Mineralogie . 7th edition. Springer Verlag, Berlin 2005, ISBN 3-540-23812-3 .
