GEMOLOGY
Monday, 22. October 2007, 19:16:16
GEMOLOGY
Topaz is a popular gem due to its attractive appearance, ready availability, and generally low price. The one exception—which is both rare and costly—is the deep yellow-orange-pink variety known as Imperial topaz. By far the most important source of this gem is the Ouro Preto area in Minas Gerais, Brazil. Unlike many other gem materials, synthetic Imperial topaz is not commercially available, and common imitations such as citrine, synthetic spinel, and glass are easily detectable.
n addition to sessions devoted to topics of major interest, the Congress will include a full slate of receptions and tours. About 3,000 people are already registered to attend the event, including members of the various international diamond bourses, government officials, bankers, and other key players in the diamond industry. The GIA Laboratory has reported on star quartz many times over the years, discussing the typical colors, cause of asterism, and sources of the material. Because this stone contained oriented needles, which caused the star, the laboratory concluded that the asterism was natural. What was unnatural, however, was the apparent color. When the bottom of the cabochon was viewed with magnification and a combination of overhead and darkfield lighting, a slightly uneven blue coating was clearly visible. In fact, two small chips near the stone’s edge revealed colorless quartz underneath
Topaz is a popular gem due to its attractive appearance, ready availability, and generally low price. The one exception—which is both rare and costly—is the deep yellow-orange-pink variety known as Imperial topaz. By far the most important source of this gem is the Ouro Preto area in Minas Gerais, Brazil. Unlike many other gem materials, synthetic Imperial topaz is not commercially available, and common imitations such as citrine, synthetic spinel, and glass are easily detectable.
n addition to sessions devoted to topics of major interest, the Congress will include a full slate of receptions and tours. About 3,000 people are already registered to attend the event, including members of the various international diamond bourses, government officials, bankers, and other key players in the diamond industry. The GIA Laboratory has reported on star quartz many times over the years, discussing the typical colors, cause of asterism, and sources of the material. Because this stone contained oriented needles, which caused the star, the laboratory concluded that the asterism was natural. What was unnatural, however, was the apparent color. When the bottom of the cabochon was viewed with magnification and a combination of overhead and darkfield lighting, a slightly uneven blue coating was clearly visible. In fact, two small chips near the stone’s edge revealed colorless quartz underneath
(100%)
WIDGETIZE