Identifying Rough Gemstones
How to spot valuable gems when they look like ordinary rocks. Lustre, cleavage, and hardness.
It Doesn't Look Like Jewelry
Rough gemstones rarely look like the cut stones in a ring. They are often coated in dirt, have rough surfaces, or look like broken glass. Learning the specific crystal habit (shape) of gems like quartz (hexagonal prisms) or garnet (dodecahedrons) is crucial.
Lustre and Fracture
Look for the way the stone reflects light (lustre). A 'glassy' or vitreous lustre is common for many gems. Also, check how it breaks. Quartz has a conchoidal (shell-like) fracture, while others might split along flat planes (cleavage).
Hardness Testing
A scratch test using the Mohs scale is a primary identification tool. If it scratches glass (hardness 5.5), it's harder than many common rocks. A pocket knife is about 5.5, a copper penny is 3.5. Real diamonds (10) will scratch everything else.
Specific Gravity
Gemstones are often denser than common rocks like quartz or feldspar. The 'heft' of a stone—how heavy it feels for its size—can be a big clue. Sapphires and garnets, for instance, feel surprisingly heavy.