|Written by Administrator|
|Tuesday, 18 September 2007|
dispersion. The property of transparent Gemstones to separate white light into the spectral colors. The interval between such colors varies in different gemstones, and is usually expressed by the measure of the difference between the refractive indices of the red ray and the violet ray. diamond has the highest dispersion (.044) of any of the popular, natural, colorless gems. See fraunhofer lines.
Di'Yag. Trade name for man-made yttrium aluminum garnet (YAC). Djevalite. Trade name for man-made cubic zirconia.
dodecahedral cleavage (doe'-dek-ah-he"-dral). Cleavage in six planes, parallel to pairs of opposite faces
of the dodecahedron. Although diamond may show such cleavage, it is not easily developed. See dodecahedron, CLEAVAGE, CLEAVAGE (IN DIAMOND).
dodecahedron (doe'-dek-ah-he"-dron). One of the seven basic forms in the highest symmetry (hexoctahe-dral) class of the cubic, or isometric, crystal system. It has 12 rhomb-shaped faces, each of which intersects two of the crystallographic axes and is parallel to the third. It is also called the rhombic-dodecahedron. See cubic system, hexoctahedral class.
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