The Chalmer's Topaz is a topaz gem weighing 5,899.5-carats located in Chicago, Illinois' Grainger Hall of Gems, in the Field Museum of Natural History. It was named for former Field Museum trustee William J. Chalmers and his wife Joan Chalmers, who established a fund used to purchase gemstones for the Field Museum collections. The Chalmers Topaz is one of the largest cut topaz gems in the world. Topazes, like diamonds, are found in both secondary and primary sources. The primary sources are igneous rocks and volcanic rocks. Some of the secondary sources, like the Brazilian stream where the Chalmers Topaz was found, are quite spectacular, with finds of single, colorless topaz crystals weighing up to several hundred pounds!
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