The name Sapphire (Greek-Blue) used to be applied to various stones. In antiquity and as late as the Middle Ages, the name sapphire was understood to mean what is today described as lapis lazuli. Around 1800 it was recognized that sapphire and ruby are gem varieties of corundum. At first only the blue variety was called sapphire, and corundums of other colors (with the exception of red) were given special, misleading names, such as "Oriental Peridot" for the green variety or "Oriental Topaz" for the yellow type.
Today corundumes of gemstone quality of all colors except red are called sapphire. Red varieties are called rubies. The various colors of sapphire are qualified by description, e.g., green sapphire or yellow sapphire. pinkish Orange sapphire is called Padparadscha (Sinhalese for "Lotus Flower").
There is no definite demarcation between ruby and sapphire. Light red, pink or violet corundums are usually called sapphires, as in this way they have individual values in comparison with other colors. If they were grouped as rubies, they would be stones of interior quality. The coloring agents in blue sapphire are iron and titanium; and in violet stones, vanadium. A small iron content results in yellow and green tones; chromium produces pink, iron and vanadium orange tones. The most desired color is a pure cornflower-blue. In artificial incandescent light, some sapphires can appear to be ink-colored or black-blue.
Through heat treatment at temperatures of about 3100-3300 degrees F (1700-1800 degrees C), some cloudy sapphires, nondistinct in color, can change to a bright blue permanent color.
Hardness is the same as ruby and also differs clearly in different directions (and important factore in cutting). There is no flourescence characteristic for all sapphires.
Inclusions of rutile needles result in a silky shine; oriented, i.e., aligned, needles cause a six-rayed star sapphire.
Deposits: Host rocks of sapphire are dolomotized limestones, marble, basalt, or pegmatite. It is mined mainly from alluvial deposits or deposits formed by weathering, rarley from the primary rock.production methods are usually very simple. The underground gem-bearing layer is worked from hand-dug holes and trenches. The separation of clay, sand, and gravel is done by washing out the gemstones due to their higher density. Final selection is made by hand. Sapphire is much more common than ruby, as the substances which lend color to sapphire are more common than those of ruby. Today economically important sapphire deposits are in Australia, Myanmar, Sri lanka, and Thailand.
Australian deposits have been known since 1870. The host rock is basalt; the sapphires are washed out of the weathered debris. Quality is modest. Under artificial light, the deep blue stones appear inky, blue-green, nearly black; lighter qualities have green tint. In recent decades black star sapphires have been found in Queensland. Accompanying minerals are pyrope, quartz, topaz , tourmaline, and zircon. Since 1918 good blue qualities have been found in New South Wales.
The alluvial deposits in upper Myanmar near Mogok are partially worked with modern methods and yield rubies and spinels as well as sapphires. The host rock is pegmatite. In 1966 the largest star sapphie was found here, a crystal of 63,000ct.
Sapphires have been found in Sri Lanka since antiquity. The deposits are in the southwest of the island in the region of ratnapura. The mother rock is a dolomo-tized limestone, which is enclosed in granite gneiss. There are also 10-20-in (30-60 cm)-thickriver gravel placers (called illam locally) that are exploited from a depth of 3-33 ft (1-10 m). Sapphires are usually light blue, with a tinge of violet.
There are also yellow and orange (Padparadscha) varieties as well as green, pink, brown and nearly colorless stones, also star sapphires. Accompanying minerals are apatite, epidote, garnet, quarts, ruby, spinel, topaz, tourmaline and zircon.
There are two sapphire deposites in Thiland: one in the region of Chantaburi, southeast of Bangkok, the other one near Kanchanaburi, northwest of Bankok. The stones are of good quality in various colors, including star sapphire. Blue sapphires have a deep color, but tend to have a tinge of blue-green.
The most desired sapphires used to come from kashmir (India), where the deposits were situated at height of 16,500 ft (5000 m) in the Zaskar mountains production varied since 1880, and the deposits have apparently been worked out. The host rock is a kaolin-rich pegmatite in crystalline schist. The decomposition product yields sapphires of deep cornflower-blue color, often with a silky sheen. most stones sold today as kashmir sapphire com from Myanmar.
In the late 1800s sapphire deposits were discovered in Montana (United States). The host rock is andesite dikes. Mining is carried out on the dike rock, also from weathered material. Color of sapphire varies and is often pale blue or steel-blue.Mining has been interrupted repeatedly since end of the 1920s, but has been steadier in recent years.
There are also significant sapphire deposits in Brazil, Cambodia, China, Kenya, Madagascar, Malawi, Nigeria, Pakistan, Rwanda, Tanzania, Vietnam, and Zimbabwe. Isolated star sapphires have been found in Finland.
Famous sapphires: Large sapphires are rare. They are sometimes named in the same way as famous diamonds. The American Museum of Natural History (New York) owns the "Star of India," perhaps the largest cut star sapphire (536ct); also the "Midnight Star," a black star sapphire (116ct). The "Star of Asia," a star sapphire weighing 330 ct, is owned by the Smithsonian Institution in Washington , D.C. Two famous sapphires (St. Edward's and the Stuart sapphire) are part of the English Crown Jewels. In the United States, the heads of presidents Washington, Lincoln, and Eisenhower have been carved out of three large sapphires, each weighing roughly 2000ct.
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