Gem, a beautiful stone, valued chiefly for personal adornment. Most gems are minerals and are more exactly called gemstones. Some gems are stonelike substances of living origin, such as pearls and jet. Gems also may be made artificially.
A gem must be polished, and sometimes shaped, to bring out its full beauty. Artistic cutting or carving can give the gem the added value of fine craftsmanship. When displayed in an appropriate setting—for example, in a gold ring—a gem is properly called a jewel.
include all the mineral gemstones. The science of gemology groups them by families according to their crystal systems or chemical composition.
A small class of natural gems—all having some mineral content—are those of animal or plant origin.
There are various kinds of artificial gems, including the following:
Imitation Gems contain no natural gem material, though many closely resemble natural gems. Most imitation stones are made of glass or plastic. Paste, a brilliant glass with a relatively high content of lead, can be made to resemble various kinds of gems.
Synthetic Gems are manufactured stones that duplicate the crystalline structure and every other property of natural gems. They differ from natural gems in minor ways, arising from the process of manufacture, that only an expert can detect.
Composite (or Assembled) Gems are made of two or more pieces, at least one of which is of a synthetic material. The pieces are cemented together to appear as a single large gem.
are natural or synthetic gems whose color or appearance has been changed by heat, irradiation, a metallic backing, or impregnation with oil, wax, dye, or other substance.
The value of gems lies mainly in their beauty, durability, and rarity. The beauty of a gem largely depends on the gem's optical qualities. The most important are: (1) luster, or brightness; (2) color; and (3) fire, the dispersion of white light into flashes of color. The durability of a gem depends on its hardness and toughness. Hardness indicates a gem's resistance to being scratched; toughness, its resistance to fracture. A gem's rarity, together with fashion, affects the demand for and cost of a gem.
Gems that have historically been considered the most valuable are commonly known as precious stones and less valuable gems as semiprecious stones. However, in practice, a high-quality semiprecious stone can be more valuable and cost more than a low-quality precious stone. Precious stones include diamonds, rubies, sapphires, emeralds, and opals. Semiprecious stones include zircons, spinel, and amethysts.
A number of early peoples believed that gems were drops of dew, raindrops, or even tears, hardened by the sun. Since the sun rises in the east, and is hottest in the tropics, the most prized gems were those that came from India and Arabia.
The list of superstitions once connected with gems is virtually endless. Amber cured disease. Amethyst assured pleasant dreams. Coral was a charm against shipwreck and fire. Ruby prevented plague, and purified one's thoughts. Stones of all kinds were said to change color as a sign of changing fortunes, or to indicate the death of the distant beloved.
Beyond superstition, yet perhaps arising from it, is symbolism. The great religions, in their rituals, early assigned special meaning to gems. Jade is associated with Buddhist worship. In Old Testament times, 12 kinds of gems, representing the Twelve Tribes of Israel, were worn in the breastplate of the high priest of Judaism. Among Christians the Twelve Apostles have been represented symbolically by precious stones. Pope Innocent III commanded his bishops to wear sapphire rings as a sign of peace.
In a more popular sense the language of gems endures in birthstones. Different gems are associated symbolically with the months of the year. Birthstone lists do not always agree. The previous page, showing cut and polished gems together with their forms in nature, uses the list of the American Gem Society and the Jewelry Industry Council. This list also recognizes alternate gems for March (bloodstone), June (pearl and alexandrite), August (peridot), October (tourmaline), and December (zircon).
The Gemological Institute of America (founded in 1931 and located in Santa Monica, California) and the American Gem Society (1934; Los Angeles, California) are organizations for the scientific study of gems and the protection of dealers and the public from gem frauds.