Step 3: Practical Gemology
Scratch testing (or hardness testing) is one of the most destructive gemstone tests. Never perform a scratch test on a finished stone. This can fracture or shatter the gem, even if tested on an inconspicuous area.
Gem rough can be scratch tested, but caution is needed. Keep in mind that the rough may have incipient fractures that can’t be seen or internal stress that will open up easily to pressure. For these reasons, scratch testing should only be performed on small protrusions. Whenever possible, saw a piece off of the main rough stone for testing.
Scratch Testing Tools
Scratch testing requires a set of pencils or rods with ends of known Mohs hardness value. Hardness sets are available commercially, or you can make your own. Get some wood dowels about the size of a pencil. Attach small, sharp pieces of synthetic corundum, topaz, and quartz to the ends of individual dowels. Label them 9, 8, and 7, respectively. For a more complete set, you can add feldspar and apatite, 6 and 5, respectively.
You don’t need any other points because minerals with the same hardness will not scratch each…