Crystalline SystemsWritten by Alain Darbellay GGGems
Continued from page 1
· Inversion by a center · Combination of rotation and inversion The crystals show in their form and their structure of properties of characteristic symmetry. And like there is a cor - respondence between reticular plans and faces of crystals, there is a fundamental correspondence between internal symmetry and external symmetry. We imagine drawing of a tapestry, it will repeat ourselves by a simple parallel displacement (translation). When a crystal is examined, first All geometrical operations which point which draws attention is a cause a repetition of pattern are certain symmetry. One can see called operations of symmetry. In repetition of faces identical to various shape of crystals (external format), places of crystal. These repetitions this translation does not appear directly. are controls by laws of symmetry, On other hand, in their morphology, Albite way in which they are repeated is determined by operators of symmetry, there are three principal types of them: Axis of symmetry, symmetry plane and center of symmetry. GGGEMS.COM ¦Gemology ¦ Corundums ¦ Tourmaline Characteristics ¦ Garnets ¦ Cutting Styles
http://www.gggems.com/crystalline_system.htm
| | Madagascar TourmalineWritten by Alain Darbellay GGGems
Continued from page 1
from pink to red, chromium and vanadium is in green tourmalines, yellow and brown one is produced by trivalent iron. Diagrammatic provision Growth zoning and geometrical drawings in a SLICED TOURMALINE of a complete crystal cut tourmaline sliced in section from Vohitrakanga. parallel to ternary axis. Rubellite Chrome Tourmalines Indigolite from Anjahamiary. Macle of green tourmaline Antsongombato type. from Tsaniria. ( Madagascar ) Estaknala ( Pakistan ) ( Madagascar ) ( Madagascar ) Sketch of Antsongombato mine ( Antsirabe area) at beginning of 20th century. The attack Mine of Alakamisy Itenina ( Fianarantsoa area). measured about fifteen meters, coal face was to This mine is worked in alluvium, first stones were hillside 10 meters above brook, it showed discovered in 1989 in a rice plantation. It produced presence of a large sill of hard pegmatite, laid out in rubellites and remarkable tourmalines with geometrical benches lities by a secondary cleavage. To wall drawings. one sees a schistous limestone greenish and broken up, to roof, one distinguishes only clay. This deposit was famous for its red-ruby tourmalines. The Mine of Anjanabonoina, located in high plateaus, produced rubellites, green tourmalines, brown-orange, pink, blue-sky, purple, and a variety of rare stones since end of 19th century. This deposit is elluvial. ¦ Cutting Styles ¦ Characteristics ¦ Crystalline Systems ¦ Madagascar Sapphire ¦ ¦ Tourmaline Polychrome ¦ Tourmaline Crystal ¦ Tourmaline Crystal 2 ¦ Tourmaline Slice ¦ Your guide to GGGems All pictures on this site have been shot by gggems.com Alain Darbellay © 1987 - 2004 gggems.com All rights reserved.
http://www.gggems.com/tourmaline_characteristics.htm
|
