Welcome to the Mineral and precious stone glossary

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The area where a particular mineral is found.

Amorphous, yellow to red substance composed of iron compounds such as Hematite and Limonite.

Three dimensional polyhedron that is a combination of a cube and octahedron.

Shaped as an octahedron.

Type of cleavage exhibited on minerals of the isometric system that crystallize as octahedrons. The method of cleavage is that flat, triangular "wedges" peel off of the existing octahedron. Example = Fluorite.

Eight sided polyhedron; all sides are equidimensional and bisect at at the same angle. Minerals shaped as octahedrons belong to the isometric system. Plural = Octahedra or Octahedrals

Any mineral that is Oolitic.

Aggregate composed of very small, spherical particles.

The present term describing something displaying opalescence.

Effect seen in a few minerals, chiefly opal (hence its name) which cause it to exhibit a glimmer of different colors when rotated or seen in different angles.

The common habit of Opal that it replaces material, such as wood, shells, and other minerals.

To be chemically altered to Opal. See Opalization

Not able to transmit light, which in effect disables it from letting an object be seen through it. (See Transparency in mineral properties for more information.)

Having to do with optics.

Physical properties of a mineral or gem that have to do with optics, such as dispersion, absorption spectra, refractive index, asterism, and dichroism, just to name a few.

Branch of physics that deals with light and the electromagnetic radiation; certain areas are dispersion, absorption spectra, reflection, and refraction.

Material which has a valuable constituent, usually a precious metal, that gives it value and makes it profitable for extraction. A fine example is Calaverite, which is extracted because of the gold it contains. "Ore" also refers to the precious material that was extracted from the ore.

Composed of carbon compounds; being from the source of living organisms.

Any mineral that falls under the following specifications belongs to the orthorhombic crystal system: Three axes, all are unequal in length. All three axes are at 90° to each other. (See Crystals in mineral properties for more information)

Bedrock revealed at the surface of the earth.

The process of undergoing a chemical change through exposure to oxygen. See also oxidize.

Minerals that form after being altered from being exposed in the oxidation zone.

Area of a deposit where the rock is exposed to air and therefore is affected by wind, rain, pressure, and air, which chemically affects the minerals embedded in the rock and alters them to secondary minerals.

Group of minerals that are compounds of one or more metallic elements combined with oxygen, water, or hydroxyl (OH). The oxide group contains the greatest variations of physical properties. Some are hard, some soft. Some have a metallic luster, others are clear and transparent. The Oxide group is divided into the Simple Oxides Hydroxides Multiple Oxides

Property exhibited in certain minerals that cause them to tarnish, or discolor upon contact with air. Also term used to describe the chemical alteration of one mineral into another mineral through oxidation.

Having gone through a chemical change as a result of exposure to oxygen.