|
Agate is a striped chalcedony quartz that forms in layers and in a wide variety of colors and textures. An individual agate forms by filling a cavity in a "host" rock. As a result, agate often is found as a round nodule, with concentric bands. In ancient times it was said to quench thirst and guard against fever, and agate bowls were very popular in historical Europe. Amethyst is an extremely sought-after gem which has been valued by many civilizations since antiquity. A variety of vitreous quartz, amethyst often forms dramatic prismatic crystals which are often formed into jewelry without being cut. Brazil and Uruguay are common sources of high quality amethyst. In the early Christian church, amethyst was believed to guard against intoxication, hence its derivation from the Greek "amethustos," meaning "not drunk." Iolite is the deep blue gem variety of the silicate mineral cordierite, named for French geologist Pierre Cordier. Iolite is found on Garnet Island in Canada and in South Asia and South Africa. Leif Eriksson and other Viking explorers are said to have used thin slices of iolite to navigate during voyages, taking advantage of its prismatic properties to polarize sunlight. Larimar is a rare gemstone found only in an inaccessible region of the Dominican Republic overlooking the Caribbean Sea. The sky blue stone's name was coined by a Dominican, Miguel Méndez, who combined his daughter's name Larissa, with mar, the Spanish word for sea. Moonstone is a variety of orthoclase, a feldspar. It often has a sky blue opalescent sheen, also called schiller or fire, making the stone look as if it is glowing. The sheen is created by thin layering of orthoclase with another mineral, albite. Moonstone was used in jewelry from 100 AD in Rome and even earlier in Asia. Natural pearls are formed when an foreign object becomes trapped in the shell of an oyster or pearl and the animal surrounds the object with several mineral layers in order to protect its soft tissue. Most pearls sold today are farmed pearls, created by intentionally inserting small mother-of-pearl beads in the oyster's shell. The resulting pearls are harvested up to two years later. Pearls come in a range of pastel colors from cream to blue to pink, and irregularly shaped pearls are often called "baroque" pearls. Mabe pearls are hemispherical cultured pearls grown against the inside shell of an oyster rather than in the mollusk's body. Mabe pearls are typically used in settings such as that conceal their flat backs. Derived from "tapaz," the Sanskrit word for fire, topaz is one of the most brilliant cut gemstones in existence. Topaz comes in a variety of colors from yellow to blue, and deeper blues and pinks are often created by heat-treating stones. Brazil is the world's top exporter of topaz.
|
