The Star Trek vision of analysing rocks and minerals with the sweep of a handheld device has taken a step towards becoming science rather than science fiction. "We are developing a tricorder," said Robert Downs, associate professor of geosciences at The University of Arizona in Tucson. Professor Downs is using a technique called Raman spectroscopy to compile a library of spectral fingerprints for all the Earth's minerals. About 1,500 of the 4,000 known minerals have been catalogued so far. Although the current Raman spectrometer takes up an area the size of a tabletop, Professor Downs's colleague M. Bonner Denton, a...