The Oriental emerald or green sapphire does not approach the beryl or true emerald in depth of color, but because of its superior hardness and brilliancy, added to its extreme rarity, it is the most valuable of green gems. The Oriental amethyst or purple sapphire sometimes reflects a red color by artificial light, and is valued highly as a gem stone; the common amethyst is softer, less brilliant, and loses by artificial light. The various other colored sapphires, such as yellow or Oriental topaz, light green or Oriental aquamarine, greenish-yellow or Oriental chrysolite, and aurora-red or Oriental hyacinth, are all valuable as gem stones when they are pure, well cut, and have pronounced colors—in fact, the name Oriental is given to distinguish the corundums from the less valuable minerals of the same colors which they resemble, but which they greatly surpass in beauty and value because of their brilliancy and superior hardness. STAR SAPPHIRES. 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. SPINEL. It is only during the past century that mineralogists make a distinction between the minerals spinel and corundum. The composition of the spinel was discovered towards the end of the last century, and was found to be about seventy per cent. alumina, twenty-five per cent. magnesia, and small parts of oxide of chrome, silica, and protoxide of iron. Up to that time, red spinels had always been confounded with rubies, and many celebrated so-called rubies have been shown to be spinels by modern mineralogists.