|Topaz||NMNH G9875-00||Minas Gerais, Brazil||22,892.5 ct|
|Topaz||NMNH 148089-00||Minas Gerais, Brazil||-|
|Topaz||NMNH 148090-00||Minas Gerais, Brazil||-|
Topaz is renowned for its ability to grow huge gem-quality crystals. Shown here are two of the world’s finest large topaz crystals weighing 31.8 kg (70 lb) and 50.4 kg (111 lb) respectively. These crystals, mined in Minas Gerais, Brazil, were originally slated to be cut up for scientific instruments, however a more suitable material was discovered. What look like gas bubbles rising inside are imprints of albite crystals that once grew against the back surfaces. Another reason that several large gem-quality topaz crystals can be found in museums is that at the time they were discovered, their pale color made them unattractive for cutting into gems. This would not be the case today as these crystals are the essential raw material for the modern blue topaz market. Exposure to radiation and then heating turns the topaz shades of blue. This treated topaz is commonly seen in jewelry today. At 22,892.5 carats, the “American Golden” topaz (center) is one of the world’s largest gemstones. It was faceted by Leon Agee over a period of two years in the late 1980’s from an 11.8 kg (26 lb) stream-rounded topaz cobble. The “American Golden” has 172 facets and measures 17.53 x 14.94 x 9.34 cm (6.9 x 5.9 x 3.7 in).
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