New Mexico Mineral Symposium — Abstracts

Although today the gem trade encourages jewelers and the public to consider all gems precious, four gems historically stood above the others with special allure, beauty, and value. Throughout the world, diamonds, emeralds, rubies, and sapphires are known as precious. They are the gems against which all others are measured.

While writing and photographing the National Geographic gemstone series for 14 years, I had the opportunity to make field trips to and do extensive work around the major mines for all four precious gems. Those experiences emphasized the similarities and differences in exploration, in the deposits themselves, and in extraction. Of the four, only rubies and sapphires, which are both corundum crystals with trace-element-induced color variations, occur together.

Diamonds are unique, not only for their unprecedented hardness and heat conductivity but because of their delivery system to the earth's surface. No matter where they were formed under the earth's crust, they have to be propelled to or near the surface via a volcano for us to ever find them. Diamonds can be profitably mined either by locating the primary source, the diamond-bearing volcanic pipe, or by locating alluvial deposits where the gems have washed. South Africa's inland mines and those in Botswana, Russia, and Australia are examples of primary deposits whereas the Namibian coast, Angola, and the Ivory Coast illustrate secondary, or alluvial, deposits.

Although tunneling is sometimes used for gems (South African diamond mines, two or three tunnels at Colombia's Muzo emerald mine, and a pair of ruby tunnels in Mogok, Burma), the vast majority of gems are extracted in opencast mines or from small operations in river or stream beds. This is in sharp contrast to ore mining and illustrates the differences between gem crystal deposits and precious metals, for instance.

Also in contrast to diamond mining, which is often done by large companies or governments, individuals and small operators mine most colored stones. In fact, to assure this occurs and that its gem deposits provide income to local workers for decades, Sri Lanka prohibits the use of machinery. In Brazil, the world's largest volume producer of emeralds, claims are only 10 x 10 m, 100 m². In Zambia, Pakistan, Afghanistan, Kenya, Tanzania, Thailand, Cambodia, and a host of Third World counties, picks, shovels, and buckets are the means for bringing gems to market.