Why do geologists have an easier time identifying gems than gemologists? Because they can more readily conduct destructive gemstone testing. Geologists can scratch gems to test their hardness, check their reaction to acids, and even put them in a torch’s flame to identify them. However, with care, gemologists can also conduct these tests.
By Donald Clark, CSM IMG 1 minute read
Cuff with turquoise stones - destructive gemstone testing

Turquoise stones are sometimes coated with thin layers of wax to improve their appearance. A hot point test on a tiny, inconspicuous spot can make any wax present bead like perspiration on the stone without actually touching its surface or damaging it. Destructive gemstone testing, like a hot point test, is a “last resort” for gemologists trying to make a difficult gem or treatment identification. When done carefully by a professional, these tests shouldn’t lessen the value of a gem or jewelry piece. Turquoise cuff with vintage beads. Jewelry and photo by Melissa Ingram. Licensed under CC By 2.0.

These destructive tests are informative but, obviously, they can damage the gems and reduce their value. Gemologists normally use complex optical and microscopic examinations to identify unknown gemstones without damaging them. Unfortunately, standard gemological tests occasionally fall short of positive identification. In these cases, gemologists must resort to destructive gemstone testing. With great care, however, these tests can be conducted in a limited manner without diminishing the value of the stone.

Destructive Gemstone Testing Series

Our five-part series on destructive gemstone tests offers concise explanations of the principal procedures.

scratch test - quartz vs calcite
A material with a Mohs hardness of 7 will scratch any material with a lower hardness. For example, this quartz (7) scratches a piece of calcite (3). Photo © Joel E. Arem, PhD, FGA. Used with permission.