Adularescence
A white or silver blue iridescent haze displayed by moonstone and other gems.

Alluvial Deposits
Gem deposits found in water after they have been separated from the mother or host rock.

Amber
A prehistoric fossil resin that usually has plants and other debris, including insects trapped inside which then hardens over thousands of years, usually found underground in areas what used to be deep forest vegetation.

Appraisal
An evaluation performed by a licensed gemologist to determine the value of a gem or item of jewelry.

Asterism
A star effect displayed by certain gems with intersecting inclusions.   (see 'rutiles')

Bruto
The Spanish word for "rough", as in rough or raw gemstone and mineral material.

Cabochon
The most common form of gem cutting, in which the mineral is cut with a flat bottom and is rounded on top.

Carat
The unit of measure for the weight of a mineral. One carat is roughly equal to 200 milligrams, or five carats equal approximately one gram.

Cataclastic Rock
A metamorphic rock produced by the crushing and grinding of pre-existing rocks, that are still visible as crushed fragments.

Chatoyancy
Cat's eye effect produced by some gemstones when cut properly in cabochon form.    (see 'rutiles')

Crystal Structure
The orderly geometric spatial arrangement of atoms in the internal organization of a mineral specimen.

Cleavage
The breakpoint or weakness of a gem, connected to its atomic structure. Most gems with perfect cleavage are more likely to break when being cut or faceted.

Color
An important property used in the evaluation of a gem. The quality of a gem can be measured based on either the presence or the absence of color.

Color of Play
Same as above, usually used to describe the fire in an opal or fire agate.

Dendrites
Skeletal crystals that develop from supersaturated solutions, often in small cracks, often resembling plants or trees.

Dichroism
The ability of some gems to display a second color when viewed from a different angle.

Dispersion
The splitting of light as it enters a gemstone. Also called a stone's "fire".

Doublet
A stone made of two components, generally held together with a clear adhesive.

Drip Stone
Stalagmites or stalactites.

Druse or Drusy
The crystal coated surface of a rock specimen.

Enhydro
A stone, geode or quartz with the center cavity containing encased water.

Facet
The cut and polished part of a gemstone.

Faceting
The process of cutting a gemstone to have multiple polished, angled flat surfaces. This process is designed to bring out the brilliance of a gem.

Fire
Characteristic of certain gemstones that disperse white light into a rainbow of colors. It is a primary characteristic of gem diamonds, opals, fire agate, spectrolite and other stones.

Fluorescence
Temporary emissions of radiation at different wavelengths (color) struck by light waves - long or short wave ultraviolet light.

Fluvial
Mineral deposits from rivers.

Foliated
A substance made up of thin leaves, like mica.

Fracture
A break with an uneven or irregular surface crack.

Gem
A mineral crystal or natural gemstone that has been cut and polished. In general, any attractive and relatively flawless mineral crystal can be cut into a gem.

Gemologist
A person who has successfully completed recognized courses in gemology and has proven skills in identifying and evaluating gem materials.

Gemology
The science, art and profession of identifying and evaluating gemstones. A branch of mineralogy.

Geode
A hollow rock cavity usually containing some form of one or more quartz gemstone. Amethyst and Peridot are sometimes found in geodes.

Gram
A unit of measurement of weight used to express the weight of a gem. Just over 28 grams equals one ounce. (one thousand milligrams equal one gram)

Heat Treatment
The application of heat to a gemstone for the purpose of improving its depth or richness of color.

Inclusion
Any type of material trapped inside a mineral during its formation. Inclusions are generally other minerals or rocks, but can also be water, gas or petroleum based.

Igneous Rock
Rock formed by the solidification of magma from a volcano.

Iridescence
The play of color in a gemstone resulting from inclusions or layers of minerals.

Carat
Unit of measurement that indicates the quantity of fine gemstone specimens and minerals like diamonds or opals.

Kilate
The Spanish word for "karat".    (see above)

Kilo
The metric measurement of 1,000 grams, or 2.2 pounds (standard measurement)

Lapidary
The art and practice of cutting gem stones and minerals.

Lapidarist
A person who is a cutter, polisher or engraver of precious stones.

Lot
A quantity of raw materials or stones, the exact weight and amount can vary.

Lote
The Spanish word for "lot".    (see above)

Luster
The outward appearance of a gem or organic material. Luster is most important especially when evaluating the quality of pearl.