Opals displaying play of color are known as Precious Opals, and opals lacking play of color are known as Common Opals. Gems can be cut from both the precious and common forms, but Precious Opal is the primary gem form of this stone. There are many varieties of both precious and common Opals. The most desired and beautiful form of opal is Black Opal, which is opal with a dark blue, dark green, or black background with a strong play of color. Next in importance is White Opal, which is Opal with a light colored body color (white, yellow, cream, etc.) with strong play of color. Also important is Fire Opal, or Mexican Fire Opal, which is a transparent to translucent deep-orange red form of Common Opal. Fire Opal can also display play of color, and this is a rarity called Precious Fire Opal.
Many precious Opals, besides being classified as either black or white Opals, are further classified based on the distribution and habit of their play of color. Some of these names have older sources, while some are recently coined trade names.
A condition called crazing affects certain Opals, causing them to form internal cracks. Crazing is an interesting phenomenon, as it lacks consistency and is sometimes unpredictable. Although it can occur at random, its often takes place when an Opal removed from damp conditions is allowed to dry too quickly, or when an Opal is exposed to sudden intense light. Crazing may also take place when an Opal is subject to vibration, as during the cutting and polishing of a gemstone. The severity of the crazing and the time it takes to "craze" varies among gemstone. The origin is often a determining factor to its resistance to crazing, as some localities are less prone to crazing than others. A gradual drying process over months or even years can in some cases effectively stabilize the stone and allow it to be cut and polished with a substantially reduced risk of crazing.
Australia is the largest producer of Opal. Other important deposits are in Ethiopia, Sudan, Hungary, Honduras, Brazil, Mexico, and the United States (Nevada, Oregon, California, Idaho).
Tourmaline, the beautiful semi-precious stone, is renowned for its extensive and exciting color spectrum. The chemical composition of this gem includes a group of closely related mineral species that share the same crystal structure. However, the presence of a complex mixture of other elements, such as calcium, manganese and iron, is primarily responsible for a tourmaline’s color.
This gem’s name is believed to have been derived from the Tamil and Sinhalese words "Turmali" or "Thoramalli" which translates to "stone with various colors". In addition to green, blue, yellow, pink, red, black and white (clear), a tourmaline is also found in bi-colors and tri-colors, with two or more shades in the same specimen.
Typically, it is the presence of iron and sometimes traces of titanium that result in blue and green tourmalines. Reds, pinks and yellows, on the other hand, are caused due to manganese.
It is believed that in the 1500s, a green tourmaline crystal was found somewhere in Brazil by a Spanish conquistador and was mistaken for an emerald. The tourmaline’s real identity, as a distinct mineral species, was confirmed by scientists only in the 1800s. New discoveries of this stone in Brazil during the 1980s and 1990s brought the spotlight on a tourmaline’s dazzling range of colors, which significantly elevated its appeal in the market.
Since tourmaline is a pegmatite mineral, it is extracted from pegmatite districts across the world, with Brazil still being the most significant source. San Diego County, including the famous Pala pegmatite district and Maine are also distributors of fine tourmalines. Malawi, in East Africa, mines striking yellow “canary” tourmalines, while blue-green tourmalines and fine rubellites can be found in Nigeria. Other sources of this gem include Afghanistan, Sri Lanka, Pakistan and Burma.
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