 
The birthstones for October are the opal or the tourmaline.Opal, admired for its distinctive play of color, is a semitransparent solidified mineral composed of silicon and water. This unique stone gets its name from the Latin opalus and Sanskrit upala (precious stone). The Greek term opallios translates "to see a change of color." There are four main types of opal (white, black, water, and fire). avalable in a variety of colors and patterns. Opal has been revered by many for centuries. The oldest known opal mine is in Czechoslovakia and dates back to the 14th century. Shakespheare praised opal as "the queen of gems" in Twelfth Night. During the 19th century, the popularity of opal suffered due in part to Sir Walter Scott's novel Anne of Geierstein, in which opal was associated with bad luck. In the late 1800s, Queen Victoria promoted Australian opals by presenting opal jewelry to her children. To-day, Australia continues to be a major opal source, supplying 85% of all the world's opals. Mohs hardness: 5.5-6.5 Refractive Index: 1.44-1.46 Specific Gravity: 2 to 2.2 The toughness of opals is poor. As they are very delicate, clean opals only with an untreated cloth. Bolder opal is a clear water opal with brilliant color play and a distinctive dark chocolate brown ironstone matrix. This intriguing gemstone formed when silica bearing steam was forced into cracks and crevices in ironstone boulders, then mineralized. Although no two opals are identical, matched boulder opals are selected for their similar color, matrix, and cut Color: Naturally ranging in shades of pinkish white to deep royal blue, these opals display an interesting mix of color. Mexican fire opal is aptly named for its brilliant red to orange body color. The color is due in part to the presence of iron oxide. Mined in Mexico, this type of opal is more lightweight than other opals, and it contains more water. Mexican fire opals tend to have one body color and do not usually contain the flashes of light and color typical of other opals. Available in translucent and transparent varieties, Mexican fire opal is the only natural opal than can be successfully faceted. The Aztec Indians of Mexico were among the first to know about this fiery gem. Europeans learned about Mexican fire opals when the Spanish conquistadors returned from the New World with this brilliant gem. The basic factors that influence an opal's value are size, cut, rarity, base color, fire color (colors produced when light is diffracted out of the stone), fire intensity, fire pattern (the pattern made by the play of color), and fire consistency. Tourmaline has been used as gem material for over 2000 years. The Chinese have long valued this beautiful gem; they've carved tourmaline ornaments for headdresses, girdles, badges, and buttons. In 1703, a package of tourmaline labeled "turmali" from Sri Lanka was sent by mistake to a stone dealer in Amsterdam. (The name tourmaline is said to have originated from this Sinhalese term). The Dutch noticed that the stones attracted ashes and straw when heated, and named the stones aschenstrekkers (ash drawers). Mohs Hardness: 7-7.5 Refractive Index: 1.624-1.644 Specific Gravity: 3.01-3.06 There are three gem varieties of tourmaline: Pink to red tourmaline is known as rubellite or elbaite. Elbaite is named after the Isle of Elba, the first known source of this stone. The pink color is due to the presence of manganese. The redder rubellite appears to be similar to a ruby. The rubellite is found in Siberia, Burma, Sri Lanka, Brazil, the United States of America (California), and Madagascar. The blue variety of tourmaline is known as indicolite. Indicolite is found in Brazil, United States (Colorado, Massachusetts, and California), Namibia, Madagascar, and the Urals. The green variety of tourmaline has no special name; therefore, it is known as green tourmaline. Green tourmaline is found in Brazil, the United States (Maine), Tanzania, Mozambique, Namibia, the Urals, and Sri Lanka. The toughness of tourmalines is good. Clean them only with jewelry cleaner, soap, or an untreated cloth.
|
