Asterism -

optical phenomenon involving the emergence of narrow streaks (bands) of light in the shape of the contracting Star on the surface of precious stones, especially polished in kaboszon. This phenomenon is caused by the presence in the crysta l lattice of the mineral inclusions, such as in the case of ruby and sapphire are the inclusions of rutile, the same as in the case of a cats eye effect. Stars asterism arising as a result are usually 4 or 6 rays, although the specimens are known in which there is 12 rays.