Cut gemstones possess all the physical properties of the mineral from which they are cut, although the crystal shape is no longer evident. If a mineral is very hard, like sapphire, the cut gem will be very durable and will scratch softer stones like quartz. If a mineral cleaves (or splits) easily upon impact, like topaz, the cut gemstone will also have this capacity, and need protection against knocks. If the mineral possesses a high degree of dispersion (the ability to split white light into its spectral colours), the gemstone will be full of 'fire', like diamond. In sphene, the gem variety of the mineral titanite, dispersion is even more pronounced.
Accordingly, gemstones are identified by the same scientific methods as minerals. However, since they are beautiful and valuable, no destructive tests that leave a mark on the stone are used. A range of scientific instruments has been devised especially for testing gemstones. People who are qualified to identify gemstones using these instruments are called gemmologists.
The Gemstone Identification Service at the Australian Museum will identify rough or cut gemstones while you wait. There is a small charge for this service. Please phone 02 9320 6240 during office hours for an appointment with Gayle Webb, Gemmologist. See Gemstone treatments.
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