Glossary of Gemology Terminology

Durability—A gemstone’s ability to withstand wear, heat, and chemicals.

Gem Species—A broad gem category based on chemical composition and crystal structure.

Gem Variety—A subcategory of species, based on color, transparency, or phenomenon.

Hardness—How well a gemstone resists scratches. Usually expressed in terms of the Mohs scale, with diamond the hardest (10) and talc the softest (1).

Inclusion—A characteristic enclosed within a gemstone, or reaching its surface from the interior.

Mineral—A natural, inorganic substance with a characteristic chemical composition and usually characteristic structure.

Mohs Scale—A scale of hardness used in classifying minerals. It runs from 1 to 10 using a series of reference minerals, and position on the scale depends on ability to scratch minerals rated lower.

Rock—A natural material composed of masses of mineral crystals of one or more kinds.

Sedimentary rock—Rock produced by the accumulation or deposition of eroded and weathered remains of existing rocks.

Thermal Shock—Damage caused by sudden, extreme temperature changes.

Toughness—How well a gemstone resists breaking and chipping.

Trace elements—Atoms in a gem that are not part of its essential chemical composition.