gems, geology, East Africa, Kenya, Tanzania, Mozambique belt, Gondwanaland

Gemstones in Gondwanaland. Gemstone localities throughout the world were studied and all districts producing more than two gem species were listed. Van Nostrand’s Standard Catalogue of Gems was consulted extensively. Excluded from consideration were: 1) diamonds; 2) gems such as opal and dioptase which can form in many geological environments via rising or descending waters; 3) gems worth less than $1 per carat; and 4) gems from one-of-a-kind localities such as Franklin, New Jersey. Emerald and amethyst had to be treated as special cases. Seventeen districts qualified for the listing, and of these, 13 were found to lie in an apparently mappable belt running across Gondwanaland. Gem mineralization in all 13 cases appears to be circa 550 million years, although some dates were obtained by inference. Other striking geological similarities were also noted. Some tentative gem correlations between East Africa and Madagascar were made based on the fine structure of the gem belt, leading to a proposed pre-drift position for Madagascar farther north than usually shown. Three of the four remaining gem districts—New York/New England, California, and Carolinas/Virginia—differ in character from the Gondwanaland belt districts and from one another. The fourth, the Urals, seems similar to the Gondwanaland belt but more data is required. Other USSR districts may exist.