Diamonds, rubies, emeralds and sapphires share at least four characteristics which class them as "precious" gemstones: transparency, hardness, rarity and beauty. Other gemstones, then, fall into the semi-precious or ornamental class of gemstone. Because the term "semi-precious" was determined to be at variance with the international gemstone standards for terminology, semi-precious stones are now referred to as ornamental. As far as I know, no one has yet argued with the term "gemstone."
Quartz is the most widespread mineral on Earth. When colorless, it is known as rock crystal and, from ancient times into the eighteenth century, it was believed to be water that had turned to stone by severe cold. The ancient Greeks learned they could create fire by focusing the sun's rays through rock crystal, and the idea that "petrified water" could create fire was one of the greatest mysteries for ancient philosophers. Priests were given sole charge of its "sacred" fire; magical properties surrounded it, and the crystal ball became a favored device of soothsayers. Almost five thousand years ago, Egyptians invented glass by perfecting a technique for melting quartz.
Amethyst is one of the colored quartz gemstones. From ancient times, it has been claimed to have mystical properties and superstition has surrounded it. Because of the legend of Bacchus, the god of wine, bishops wore amethyst on their fingers as a symbol of temperance. Bacchus is supposed to have fallen in love with Amethyst, one of Diana's nymphs, and to protect her from his advances, Diana transformed her into a pure, and inaccessible, rock crystal. Brokenhearted, Bacchus poured his goblet of wine over the stone which immediately turned purple.
Because of its pale blue color, Aquamarine is associated with water and, it is claimed, mermaids leave it on shore. It symbolizes good luck and happiness and is often carried by those going on ocean voyages.
Traditionally, the most beautiful turquoise has come from the orient and, according to legend, has protected those who wore it against curses, evil spirits and falling. In Pre-Colombian America, turquoise was so sacred, only the Aztec emperor was allowed to wear it.
The ancient Egyptians used lapis to decorate their royal tombs and, it is believed, they invented enamel in an effort to copy it. Introduced into Europe in the fifth century, it was used to produce the ultramarine blue pigment in paint.
Four thousand years before Christ, Egyptian women used powdered malachite and red ochre as a cosmetic to enhance their eyes. During the middle ages, malachite was claimed to have medicinal properties and was used, among other things, to treat colic. Wearing it was supposed to ward off lightening strikes and to aid sleep by preventing nightmares.
The patterns formed in agate, likened to shrubs, led ancient alchemists to believe it would help woodcutters to fell trees. Peasants, believing it would assure them of a good harvest, tied agate to their waists, and Persians used it to ward off storms and lightning. And, while it was used to treat the effects of snakebite, it was also used to inflame the feelings of love.
Garnet was worn by the Crusaders and given a place of honor in the Court of King Clovis of France. Believed by alchemists to have curative powers, garnet was used in the treatment of depression, then called melancholia, and because of its blood-red color, thought it able to stop bleeding and ease the complications of child-birth.
While gemstones may be found just about anywhere, significant numbers of stones are generally found in specific types of rock formations and deposits:
Diamonds are found in kimberlite pipes, vertical, pipe-like cavities formed in volcanic rocks low in silica and high in magnesium.
Aquamarine, amazonite, chrysoberyl, smoky quartz, topaz and tourmaline are found in pegmatites. Found within coarse grained rocks, pegmatites are fissures, veins and geodes having the same composition as the gemstones forming within them.
Alexanderite, garnet, lapis lazuli, ruby and sodalite may be found in metamorphic rock formations, those rocks formed when the earth's crust shifted causing an increase in pressure and temperature. For the last six thousand years, the only place lapis has been mined is from the deposit at Sar-e-Sang, Afghanistan.
Peridot and sapphire may be found in volcanic rocks. Also found in volcanic deposits, agate, amethyst, chalcedony, jasper, opal and rock crystal may form in cavities created in the molten lava by gas bubbles.
Agate, amethyst, rhodochrosite and rock crystal may also form in the hydrothermal veins which allow liquid and gas to escape from below the earth's surface. Huge deposits of amethyst have been found in Brazil and Uruguay.
Opals may be found in fissures in sandstone and limestone. These rocks, called sedimentary rocks, were created from sediment deposited by water.
Chrysocolla, malachite and turquoise are found where copper minerals have become exposed to the air. In what is called the oxidation zone, these minerals are transformed by exposure to oxygen.
Chrysoberyls, diamonds, garnets, rubies, sapphires, spinels, topazes and zircons may be deposited in streams. When the rocks that hold them weather away, the gemstones are released and washed away by the rains into rivers and streams. If they then collect in one area in the streambeds, these are called alluvial deposits.
Unakite was first discovered in the United States in the Unakas mountains of North Carolina. It can be found as pebbles and cobbles from glacial drift in the beach rock on the shores of Lake Superior. It is the state stone of Virginia, where it is found in the river valleys having been washed down from the Blue Ridge Mountains. Unakite is not limited to the United States.