Diamonds: a babe of 628 million tears.

While diamond lovers covet the clearest possible gems, geologists search the world over for stones marred by imperfections, because the impurities pack secrets about how diamonds form. A novel study of minerals trapped within one gem has now revealed the youngest known diamond, report Peter D. Kinny of the Curtin University of Technology in Perth, Australia, and Henry O.A. Meyer of Purdue University in West Lafayette, Ind.

The diamond, from Mbuji Mayi, Zaire, has an age of 628 million years, far younger than all previously dated diamonds, which range in age from 3.2 to 2.4 billion years.

"This suggests that diamonds have formed throughout geologic time and it wasn't just [early] periods when diamonds formed," says Meyer, who adds that diamonds are most likely still forming in Earth's mantle. He and Kinny discuss their research in the July JOURNAL of GEOLOGY.

In the past, geologists have dated diamonds by analyzing an aggregate of several mineral inclusions taken from different gems found in the same location. Kinny and Meyer analyzed only a single inclusion from one diamond, using a unique machine called the secondary high-resolution ion microprobe, or

SHRIMP. Housed at the Australian National University in Canberra, SHRIMP sends a beam of ions that vaporizes a sample, which then passes through a high-resolution mass spectrometer. By measuring the amounts of uranium and lead isotopes, the scientists can use the radioactive decay of uranium as a clock to date the diamond.

Diamonds develop at depths of 200 kilometers under stable continental regions, where temperature and pressure conditions combine to force carbon into its extremely dense form. After resting there for millions or billions of years, the gems are brought to the surface by extremely fast volcanic blasts called kimberlite eruptions.