WASHINGTON, July 18 (UPI) -- Scientists say they have found the first naturally occurring sample of a mineral thought to exist only deep within the Earth. But they found it in a very unlikely place ... in a rock that fell from outer space.

Researchers report in today's issue of the journal Science they discovered the mineral magnesium silicate-ilmenite in a meteorite found in Africa in 1989. Until now, scientists have only been able to study samples produced in the laboratory under extreme temperatures and pressures.

Thomas G. Sharp, lead author of the paper, says scientists believe this type of ilmenite is an important part of the Earth's mantle. Sharp, from Arizona State University, points out that it is rare to find samples of materials from the mantle, which lies hundreds of miles beneath the surface of the planet. Such materials usually are found only in small quantities as impurities in diamonds.

Sharp says this type of mineral normally would be formed deep within the Earth over an extended period of time. He says the sample of magnesium silicate-ilmenite found in the meteorite, however, would have formed quickly when the meteorite struck another object in outer space, creating extremely high pressures in the rock.

The researchers found other materials in the same meteorite that may represent remnants of magnesium silicate-perovskite, another high-pressure mineral thought to be the most common mineral in the Earth's mantle.

Sharp said these findings reinforce the idea that meteorites can offer scientists a new place to look for unusual minerals. The research also may help scientists understand the effects of the shock of high-velocity impacts in minerals.

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