IGI
Stands for the "International Gemological Institute". It is the largest independent gem certification and appraisal service in the United States.

Igneous
A substance produced under conditions involving intense heat, such as that which is found in volcanoes. Igneous rock is rock formed by solidification from molten magma.

Imperial Jade
Imperial jade is another name for emerald jade. It is a fine emerald-green color.

Imperial Topaz
Imperial topaz is golden orange-yellow topaz; it is the most valuable type of topaz.

Imperial Mexican Jade
Imperial Mexican jade is not jade at all; it is calcite that has been dyed green.

Import
The act of bringing or carrying in goods from an outside source for trade or sale, especially in regards to goods from a foreign country.

Inca Emerald
Inca emerald is an emerald that is mined in Equador.

Inclusion
A naturally occurring flaw, (feather, fracture, fissure, carbon spot, or cloud), within a diamond or other stone. The test for clarity looks for these flaws.

Indian Agate
Indian agate is another term for moss agate.

Indicolite
Blue Tourmaline.

Ingot
Metal cast into a bar or other shape.

Inlaid
Past tense of inlay.

Inlay
A decorative technique in which part of the surface of a piece of jewelry, furniture, or ceramic is cut away and stone, mother of pearl, or some other substance is imbedded into the hollowed-out area so that it is level with the surface of the piece. See also channel inlay.

Intaglio
Italian for "carving", an Intaglio is a carved gem wherein the design is engraved or carved into the object so that it sits below the surface plane of the material, as opposed to a cameo in which the design is raised from it's background, in relief. This technique was often used for seals, which made a raised impression in wax used to seal a letter or authenticate a document. It was commonly attached to watch fobs, since the watch fob is a good manner of carrying a seal. Once seals fell out of common use, the intaglio tended to face out to the viewer rather than down as on a seal. Some of the most commonly found Victorian intaglios were carved in carnelian, an orange-brown variety of chalcedony.

Intergrown
Intergrown crystals occur when two mineral crystals grow together and become one.

Inverall Sapphire
Inverall sapphires are a type of sapphire from Inverall, New South Wales

Investment Compound
An investment compound is a refractory material (it can withstand extreme heat) which is slightly porous (so that gases from molten metal can escape) and can be formed into a mold (which will be used in metal casting). An example of an investment compound is plaster of paris mixed with silica, boric acid, and graphite.

Invisible Necklace
An invisible (or floater) necklace looks as though the beads are simply floating on the skin; the beads or pearls are strung far apart from one another on an almost invisible string (like clear fishing line).

Invisible Set
A method of setting square gemstones side by side in two or more rows within a metal border or frame so that they are flush against one another with no metal separating them.

Iolite
(also called dichroite or water sapphire). A silicate of alumina, iron, and magnesia which is usually violet-blue, but can be deep blue, light blue-gray, and yellow-white. Makes a beautiful transparent gemstone which is remarkable for its dichroism.

Iridescent
A display of lustrous rainbow-like colors. The colors seen in an oil slick or mother of pearl are good examples of iridescence. Synonymous with "Pearlescent".

Iridium
A metal of the platinum family often alloyed with platinum to improve workability. Pieces marked "80% Plat. 20% Irid" would indicate that the alloy is 80 % platinum and 20% iridium.

Irish Diamond
Irish diamond is not a diamond at all; it is rock crystal from Ireland.

Iron
The most common metallic element which usually appears dark brown, from oxidation or impurity, but when pure is silvery-white. Iron is found abundantly in nature, usually in combined forms such as hematite, limonite, magnetite, and taconite. It is frequently alloyed in a wide range of important structural materials like cast iron, steel, and wrought iron. It is easily oxidized (rusted) by moisture, and is attacked by many corrosive agents.

Iron Pyrite
See Pyrite.

Irradiated Diamons
Irradiated diamonds are diamonds that have been exposed to radiation. This changes the diamond's color (as the radiation changes the crystalline structure of the diamond). The change in the diamond is permanent. Older radiation treatments involving exposing the stone to radium; newer treatments bombard the stone with atomic particles in a cyclotron (which accelerates protons, neutrons, or alpha-partices to high speeds). The irradiated stones take on a greenish or an aquamarine hue. Irradiations of diamonds was first done in 1904 by Sir William Crookes, who exposed diamonds to radium, giving them a permanent greenish color; his diamonds are still slightly radioactive (at the level of radium-painted watch). Newer irradiation techniques bombard the crystal with atomic particles in a cyclotron, and then the stone is heated to about 800 degrees Centigrade, producing a stone with very little radioactivity and a permanent color change.

Irradiation
The process of bombarding a gemstone with X-rays, gamma rays or streams of subatomic particles in order to change the stone's color.

Italian Lipis
Italian lapis is not lapis; it is actually blue-dyed jasper from Italy.

Ivoride
See French Ivory.

Ivory
A hard, smooth yellowish-white substance made from the tusks of elephants and walruses.

Ivory, French
See French Ivory.