Since corundum is easily manufactured, synthetic ruby and sapphire are used extensively in jewelry. The synthetic stones can be distinguished from natural stones by microscopic examination of the kinds of inclusions and internal defects. VARIETIES Ruby: Red. Sapphire: Blue, yellow, pink, green, colorless, and any color except red. Star sapphire: Colored as sapphire and showing asterism. Star ruby: Red and showing asterism. BERYL (INCLUDES EMERALD AND AQUAMARINE) Beryl is probably the most widely used colored gemstone, and under its several names in the gem world it is probably the best known. When it is a rich green it is known as _emerald_, and when it is the blue-green of sea water it is called _aquamarine_. Varieties such as the rose-pink _morganite_, golden-yellow _heliodor_, and colorless _goshenite_ are less well known than emerald and aquamarine but are equally attractive and satisfactory gemstones. Beryl is beryllium aluminum silicate. It frequently occurs in well-formed hexagonal crystals, and its many colors result from the presence of very small percentages of several different elements. Emerald owes its rich green color to traces of chromium, and the detection of this element is one of the means of identifying true emerald. Aquamarine, comprising the green and blue-green beryls, gets its color mainly from traces of iron. Practically all of the deep blue aquamarine available in jewelry stores results from the heat treating of greenish beryl or certain yellow-brown beryls. The stones are heated carefully to about 800° F., and the color change is permanent. The element lithium accounts for the color of pink beryl. As with aquamarine, the color of yellow beryl is now considered to be the result of traces of iron rather than uranium, as previously thought. Pure beryl is colorless. Beryl usually is found in pegmatites, which are very coarse-grained granite rocks formed by the cooling of molten material far beneath the earth’s surface. As the rock cools and beryl and other crystals are formed, the stresses introduced are so great that the crystals frequently shatter so badly they are useless as gem material. Frequently, too, impurities are introduced during crystal formation, and consequently the gem materials are found only where the crystals were able to form without interference—such as in openings or cavities in the rock.