Crystal Moonbeams- page 1 | Science | Smithsonian

Crystal Moonbeams

A pair of Mexican miners stumble upon a room filled with what could be the world's largest crystals

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Deep below the surface of an isolated mountain range in Mexico sit two rooms of splendor: translucent crystals the length and girth of mature pine trees lie pitched atop one another, as though moonbeams suddenly took on weight and substance.

In April 2000, brothers Eloy and Javier Delgado found what experts believe are the world’s largest crystals while blasting a new tunnel 1,000 feet down in the silver and lead Naica Mine of southern Chihuahua. Forty-year-old Eloy climbed through a small opening into a 30- by 60-foot cavern choked with immense crystals. "It was beautiful, like light reflecting off a broken mirror," he says. A month later, another team of Naica miners found an even larger cavern adjacent to the first one.

Officials of the Peñoles company, which owns the mine, kept the discoveries secret out of concern about vandalism. Not many people, however, would venture inside casually: the temperature hovers at 150 degrees, with 100 percent humidity.

"Stepping into the large cavern is like entering a blast furnace," says explorer Richard Fisher of Tucson, Arizona, whose photographs appear on these pages. "In seconds, your clothes become saturated with sweat." He recalls that his emotions raced from awe to panic.

Fisher says a person can stay inside the cave for only six to ten minutes before becoming disoriented. After taking only a few photographs, "I really had to concentrate intensely on getting back out the door, which was only 30 to 40 feet away." After a brief rest, he returned for another couple of minutes. "They practically had to carry me out after that," Fisher says.

Geologists conjecture that a chamber of magma, or superheated molten rock, lying two to three miles underneath the mountain, forced mineral-rich fluids upward through a fault into openings in the limestone bedrock near the surface. Over time, this hydrothermal liquid deposited metals such as gold, silver, lead and zinc in the limestone bedrock. These metals have been mined here since prospectors discovered the deposits in 1794 in a small range of hills south of Chihuahua City.

But in a few caves the conditions were ideal for formation of a different kind of treasure. Groundwater in these caves, rich with sulfur from the adjacent metal deposits, began dissolving the limestone walls, releasing large quantities of calcium. This calcium, in turn, combined with the sulfur to form crystals on a scale never before seen by humans. "You can hold most of the crystals on earth in the palm of your hand," says Jeffrey Post, a curator of minerals at the Smithsonian Institution. "To see crystals that are so huge and perfect is truly mind-expanding."

In addition to 4-foot-in-diameter columns 50 feet in length, the cavern contains row upon row of shark-tooth-shaped formations up to 3 feet high, which are set at odd angles throughout. For its pale translucence, this crystal form of the mineral gypsum is known as selenite, named after Selene, the Greek goddess of the moon. "Under perfect conditions," says Roberto Villasuso, exploration superintendent at the Naica Mine, "these crystals probably would have taken between 30 to 100 years to grow."

Until April 2000, mining officials had restricted exploration on one side of the fault out of concern that any new tunneling might lead to flooding of the rest of the mine. Only after pumping out the mine did the level of water drop sufficiently for exploration. "Everyone who knows the area," says Fisher, "is on pins and needles, because caverns with even more fantastic crystal formations could be found any day."

Previously, the world’s largest examples of selenite crystals came from a nearby cavern discovered in 1910 within the same Naica cave complex. Several examples from the Cave of Swords are exhibited at the Janet Annenberg Hooker Hall of Geology, Gems, and Minerals at the Smithsonian’s National Museum of Natural History.

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