By Michael Ray Taylor, Discovery News

Feb. 8, 2001 — The largest natural crystals on Earth have been discovered in two caves within a silver and zinc mine near Naica, in Chihuahua, Mexico, according to mine officials.

Reaching lengths of over 20 feet, the clear, faceted crystals are composed of selenite, a crystalline form of the mineral gypsum.

"Walking into either of these caves is like stepping into a gigantic geode," said Richard D. Fisher, an American consultant with the mining company to develop the discoveries as tourist attractions.

Fisher said that most people can endure only a few minutes in the caves due to their high temperatures. The smaller of the two, which is about the size of two-bedroom apartment, is 100 Fahrenheit. The large chamber, which Fisher describes as the size of a Cathedral, is 150 F. Both are located approximately 1200 feet below the surface.

The largest previously known crystals were found in the nearby Cave of the Swords, part of the same mine system. Some of these are now on display at the Smithsonian Institution. The local government and mine owners hope to avoid removing any of the new discoveries for museum displays or private collections, Fisher said.

While the mine company is currently limiting visitation of the caves to scientific experts, mineral hunters have destroyed locks and broken into the chambers twice since they were first opened by mining equipment last April. One man was killed when he attempted to chop out a gigantic crystal that fell from the ceiling and crushed him, according to Fisher.

"We need more onsite protection of mine caves," said geologist Carol A. Hill, co-author of the book Cave Minerals of the World, who calls the new discoveries "by far the largest selenite crystals I have ever heard of."