Madagascar AmethystWritten by Alain Darbellay GGGems
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Certain minerals present sometimes left forms sometimes right forms. The most known example is that of quartz. The distinction between left quartz and right quartz has a certain importance in electronics industry where one uses piezo-electric properties of this mineral. The negative crystals of hexagonal shape can contain liquids like water, gas, as well as rutile needles, tiny hematite discs, goetite, fushsite or mica. Inclusions of H2O and CO2 in an amethyst from Madagascar. Habitus type of flattened Dauphiné. This marvellous Bi-terminated amethyst of 128 grams also contains water drops in its center. Habitus type of rhomboedron. Enlarge The amethyst scepters are also typical in Madagascar. Here, a scepter in blackberry shape. There, stem of scepter developed by crystallizing around it a quantity of small points in hedgehog. Length:40 mm. Double scepter. Enlarge Head of scepter: 132 grams Enlarge Amethyst in castle on its quartz gangue. 986 grams. Enlarge The fact that sometimes only a thin surface layer of violet color be presents in stone or that this color is not homogeneous, makes often a difficult cutting. The art of lapidary is to place color correctly in order to make homogeneous tone of cut stone. The distribution of color in a cut stone is observed simply by immersing it in water contained in a transparent container and colourless. The color of amethyst varies from purple reddish to purple bluish while passing by straightforwardly crimsons tone. Thus of very variable intensity, color is often laid out in stripes parallel to final faces of crystal. Enlarge ¦ Cutting Styles ¦ Characteristics ¦ Crystalline Systems ¦ ¦ Amethyst Crystal 1 ¦ Amethyst Crystal 2 ¦ Amethyst Scepter ¦ Faceted Amethyst ¦ gggems.com © 1987 - 2004 gggems.com All rights reserved.
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| | Crystalline SystemsWritten by Alain Darbellay GGGems
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· 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
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