a. 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
b. A starlike effect observed in certain minerals either by transmitted or
by reflected light. AGI
c. 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
Dictionary of Mining, Mineral, and Related Terms