Mineralogy Glossary
Essential terms and definitions for mineralogy and mineral collecting.
Gemology
Asterism (Gem)
The star-shaped optical phenomenon in star rubies, star sapphires, and star garnets, caused by oriented …
Brilliance
The white light returned from the interior and surface of a faceted gemstone to the …
Cabochon
A gemstone cutting style producing a smooth, domed top and flat or slightly convex back, …
Carat
The unit of weight for gemstones, equal to 0.2 grams. One carat is divided into …
Chatoyancy (Gem)
The mobile bright band seen in cat's-eye gems such as chrysoberyl cat's-eye, caused by reflection …
Clarity
A grading measure of the absence of inclusions and blemishes in a gemstone. The GIA …
Color Zoning
Uneven distribution of color within a gemstone, often in distinct bands or patches reflecting growth …
Crown
The upper portion of a faceted gemstone, above the girdle. Crown height and angle affect …
Cut Grade
An assessment of how well a gemstone has been fashioned, evaluating proportions, symmetry, and polish. …
Dispersion (Gem)
The difference in refractive index between red and violet light in a gemstone, quantified as …
Facet
A flat, polished surface deliberately cut on a gemstone to reflect and refract light. The …
Fire
The display of spectral colors (red, orange, yellow, green, blue, violet) produced by the dispersion …
Girdle
The narrow band around the widest part of a faceted gemstone, separating the crown from …
Inclusion
Any internal feature within a gemstone, including crystals, needles, clouds, feathers, or growth irregularities. Inclusions …
Loupe
A small magnifying lens used by gemologists to examine stones. Standard gem loupes are 10× …
Pavilion
The lower portion of a faceted gemstone, below the girdle. The pavilion angle is critical …
Pleochroism (Gem)
The display of different colors in different crystallographic directions, important in gem cutting decisions. Tanzanite …
Refractive Index (Gem)
A key gemological property measured with a refractometer to help identify gem species. Values range …
Table
The largest and topmost flat facet on a faceted gemstone. The table percentage (table width …
Treatment
Any process applied to a gemstone to improve its appearance or durability after mining. Common …