The name girasole is applied to those gems that exhibit a peculiar radiance when exposed to the sunbeams. This curious play of light is seen in the transparent and translucent stones, but especially in the translucent. When the gem which possesses this quality is cut in the boss form it shows a glimmering light brighter at one part than at another, owing to a peculiar internal refraction. The effect is very beautiful when the gem is of fine color, and the bright spot moves mysteriously over a more sombre ground as the stone is turned in various directions. The sapphire rarely shows this property to the same perfection exhibited by one of the varieties of opal. We have seen two specimens from the North Carolina corundum mines, which would have been very superior gems if they had not been traversed in all directions by numerous cleavage planes. They were quite an inch in diameter, of a nodular form, and had been deposited in a ledge of ripidolite. One of the most remarkable varieties of the sapphire is known as the asteria, which was so named by Pliny from the fact of its displaying diverging rays of light. This phenomenon is only seen in stones of semi-opacity or inferior clearness, and the star-like rays are so arranged as to be inclined to each other at an angle of 60 degrees. These stones may be of various colors,--blue, red, or gray,--yet the rays of the star are always white or faintly tinged, and stream forth in beautiful contrast to a ground of delicate blue or decided red. The stars appear the most distinctly to view when the polished gem is exposed to direct sunlight or a small bright flame. This mysterious play is seen in but few of the gems, and the sapphire exhibits it in its greatest perfection. It is indeed a curious thing to see a six-rayed star with long silken beams of light suddenly appear to view as the gem is turned to the light, and as quickly disappear as the focus is changed. No wonder the ancients believed the appearance due to supernatural powers. The microscope, however, has disclosed to the moderns the cause of the asterism. This instrument reveals multitudes of minute crystals within the stone, arranged in three different but equal angles. To obtain the stellate appearance in perfection, then, the stone must be cut and polished in cabochon or dome-like form. The apex of the gem is then in a direct plane to these angles, being perpendicular to the axis of the primitive form of the crystal, and therefore the rays of light are reflected from the sides of these multitudinous crystals producing the asterism.