Glosarium Mineralogi

Brilliance

The white light returned from the interior and surface of a faceted gemstone to the …

Carat

The unit of weight for gemstones, equal to 0.2 grams. One carat is divided into …

Fire

The display of spectral colors (red, orange, yellow, green, blue, violet) produced by the dispersion …

Crown

The upper portion of a faceted gemstone, above the girdle. Crown height and angle affect …

Loupe

A small magnifying lens used by gemologists to examine stones. Standard gem loupes are 10× …

Table

The largest and topmost flat facet on a faceted gemstone. The table percentage (table width …

Facet

A flat, polished surface deliberately cut on a gemstone to reflect and refract light. The …

Girdle

The narrow band around the widest part of a faceted gemstone, separating the crown from …

Cabochon

A gemstone cutting style producing a smooth, domed top and flat or slightly convex back, …

Inclusion

Any internal feature within a gemstone, including crystals, needles, clouds, feathers, or growth irregularities. Inclusions …

Pavilion

The lower portion of a faceted gemstone, below the girdle. The pavilion angle is critical …

Dispersion (Gem)

The difference in refractive index between red and violet light in a gemstone, quantified as …

Refractive Index (Gem)

A key gemological property measured with a refractometer to help identify gem species. Values range …

Chatoyancy (Gem)

The mobile bright band seen in cat's-eye gems such as chrysoberyl cat's-eye, caused by reflection …

Pleochroism (Gem)

The display of different colors in different crystallographic directions, important in gem cutting decisions. Tanzanite …

Color Zoning

Uneven distribution of color within a gemstone, often in distinct bands or patches reflecting growth …

Treatment

Any process applied to a gemstone to improve its appearance or durability after mining. Common …

Cut Grade

An assessment of how well a gemstone has been fashioned, evaluating proportions, symmetry, and polish. …

Asterism (Gem)

The star-shaped optical phenomenon in star rubies, star sapphires, and star garnets, caused by oriented …

Clarity

A grading measure of the absence of inclusions and blemishes in a gemstone. The GIA …