Crystalline SystemsWritten by Alain Darbellay GGGems
© 2004 gggems.com All rights reserved. 7 systems of crystallization: There are 32 possibilities of combinations of elements of symmetry (axis of rotation, symmetry plane, centers combined inversion and operations). Since discovery of crystals reticular structure, one could show by calculation that to these 32 classes which relate to shapes of crystals, correspond 230 types of network. One immediately realizes complexity of reasoning which should be made to know all possible combinations. The 32 classes are grouped in 7 systems. Here are figures. CUBIC SYSTEM QUADRATIC SYSTEM HEXAGONAL SYSTEM Go to Garnet Go to Zircon Go to Apatite Diamond, garnet, spinell. Zircon Beryl, Apatite -------------------------------------------------- TRIGONAL SYSTEM ORTHOROMBIC SYSTEM MONOCLINIC SYSTEM (Subdivision of hexagonal system) Go to Topaz Go to Orthoclase Go to Corundum Go to Tourmaline Calcite, corundum, tourmaline, quartz. Chrysoberyl, topaz Orthoclase ------------------------------------------------- TRICLINIC SYSTEM The symmetry of crystals : appear following symmetrical operations: > > · Rotation · Inversion by symmetry plane
| | Madagascar TourmalineWritten by Alain Darbellay GGGems
© 2004 gggems.com All rights reserved. (Na, Li,Ca) (Fe2, Mg, Mn, Al)3 Al6 I(OH)4 I (BO3)3ISi6O18I · Crystallographic properties: Trigonal. Hardness 7 - 7.5 Density 3.02 to 3.26 Refractive index: 1.62 - 1.64 · Chemical Properties: Alumina borosilicate with fluorine. Occurences: In acid magmatic rocks and associated pegmatites, limestones and schists, placers. Coloured tourmalines are related to sodolithic pegmatites. One distinguishes two principal types of tourmalines: hexagonal type and triangular one. · The hexagonal type is especially characterized by presence, in prismatic zone, of well developed S1 faces, and those of L always narrow. When crystals Bi-terminated, one finds with one of ends of ternary axis rhomboedron R, and with other same rhomboedron combined with that (0111) = P. · The triangular type, here is never finished at two ends, it is characterized by prevalence of faces I in prismatic zone, while those S are very narrow just as those S2 which accompany them. The crystals on finished end carry base C, combined with rhomboedron R; in same way sometimes with rhomboedron P and base C 1 2 3 4 Fig. 1& 2 : Triangular type Fig. 3 & 4 :Hexagonal type Very rare type of Rubellite from Antsongombato tourmaline: white head and red body. 5 6 Crystal of hexagonal type finished Polychrome tourmaline being in Tsilaizina, Madagascar. at a peak frequently found in Tsilaisina. Liddicoatite Tourmaline Deep-PinkTourmaline Blue-greenTourmaline. Indigolite from Anjanabonoina. Antsongombato type. ( Kunar valley, Afghanistan.) · Colors of tourmalines: Blue is due to bivalent iron, (magnesium gives a clearer blue) manganese produce tone
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