The following tips for identifying have come from an article at https://www.thespruce.com/identifying-and-testing-jet.
- Jet will be opaque black in appearance and will not have mold lines, so the first test is to inspect it visually.
- It was also hand carved so no two pieces will be identical.
- Most jet was highly polished, but pieces made for first mourning will be matte black.
- Natural jet will be very light in weight in comparison to French jet, which is actually black glass.
- It will also be room temperature rather than cold like glass. It's also interesting to note that jet will not scratch glass, but glass will indeed scratch jet.
- Test by scraping an inconspicuous area on a rough surface like the back of a ceramic tile or the bottom of a piece of unglazed porcelain. If it leaves a brown mark, the piece is likely jet (although vulcanite can also leave a brown mark, so be sure to look for other jet attributes before making that call).