Asterias or star stones are corundums of three different colors; the
star sapphire proper is a grayish blue, the star ruby red, and the star
topaz yellow.
These stones are usually cut cabochon or convex, and display under the
rays of the sun, or when exposed to one candle or other artificial
light, a beautiful star with six points.
This star is produced by foreign substances in the corundum, and the
lapidary brings about the regular effect by cutting a pointed carbuncle
so that the centre of the star begins at the apex, and the six bright
stripes radiate to the base of the stone.
The bright lines of the star following the light move over the surface
of the stone and produce a remarkable effect. These stones are amongst
the most wonderful of mineral productions, and good specimens are very
valuable.
The corundum cat’s-eye, called Oriental girasol or sunstone, has a
bluish, reddish, or yellowish reflection of light of a lighter shade
than the stone itself, and which moves on the convex surface of the
stone like the lines of a star stone.