Asterism

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  1. Starlike rays of light observed in some minerals when viewed from certain directions, particularly if the mineral is cut en cabochon. Minerals having this feature are called asteriated or star. Asteriated beryl, chrysoberyl, crocidolite, emerald, quartz, ruby, and sapphire are known. Hess
  2. A starlike effect observed in certain minerals either by transmitted or by reflected light. AGI
  3. Elongation of Laue X-ray diffraction spots produced by stationary single crystals as a result of internal crystalline deformation. The size of the Laue spot is determined by the solid angle formed by the normals to any set of diffracting planes; this angle increases with increasing crystal deformation, producing progressively elongated (asteriated) spots. Measurements of asterism are used as indicators of deformation in crystals subjected to slow stress or to shock waves. CF: corundum cat's eye
    Source: Dictionary of Mining, Mineral, and Related Terms


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