An interesting bit of news from New Scientist at
http://www.newscientist.com/news/news.jsp?id=ns99994568
"The technique looks for lines in emerald spectra that correspond to
deuterated water, in which one of the hydrogen atoms of the water
molecule is replaced by its isotope deuterium. Atoms of different
rare-earth elements that are present strain the water bonds,
producing up to five additional bands in the pattern.
The group collected samples from 46 emerald mines worldwide and
found that their spectra fell into five different groups that
corresponded to geographical regions. Even within a group there were
differences between individual mines, the team reports in a paper to
be published in Applied Spectroscopy.
The researchers have already used the method to show that a
supposedly Colombian emerald for sale at a gem fair in Basle,
Switzerland, was in fact from Afghanistan."