r STAR-STONE. This name is given to certain varieties of the perfect corundum, when cut in a peculiar manner. The structure of this gem is that of a hexagonal prism, surmounted by a double hexagonal pyramid, which, when cut perpendicular to the axis, and rounded off in the form of a ring-stone, very often presents, when held up to a strong light, a distinct star of six rays. This phenomenon frequently occurs in sapphires and rubies, and, when perfect, the gem is highly prized.

The same name has been given to the joints of an extraneous fossil, merely from the form they present.