Glossary
of Terms

Mineral Terms A-Z

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Chemical Composition

The elements and the quantity of the elements a substance contains.

Colour

The characteristic color or colors present in a mineral.
See Color in Mineral Properties.

Crystal Habit

The three dimensional form exhibited by a mineral, with defined sides and angles which are positioned based on its inherent atomic structure.
The typical crystal formation of a mineral.

Crystal System

The primary method of classification of crystals. The crystal system classifies crystals into six distinct groups. They are:

• Isometric
• Tetragonal
• Hexagonal (which includes Trigonal)
• Orthorhombic
• Monoclinic
• Triclinic
  

The crystal class, which classifies crystals into 32 crystal types, is a more specific classification of crystal groupings.

Fracture

The characteristic way a mineral breaks when put under stress, aside from cleavage.

Indices of Refraction

The amount of refraction that takes place in a particular substance, which is a direct connection to the speed of light in that substance. The higher the refractive index, the greater the amount of dispersion, which increase the brilliance of a material. The refractive indices of gemstones are measured with a refractometer, which can often identify them.
See Refractive Index in Mineral Properties

Mohs Scale Hardness

A measurement devised by Austrian scientist Fredrick Mohs to determine the hardness of a mineral.
The resistance of an object to scrapes and scratching. The harder it is, the greater its resistance.
See Hardness in Mineral Properties for additional information. >

Optical angle

Describing the physical properties of a mineral or gem that have to do with optics, such as dispersion, absorption spectra, refractive index, asterism, and dichroism.

See The Optical Properties of Minerals for additional information.

Optical Properties

Describing the physical properties of a mineral or gem that have to do with optics, such as dispersion, absorption spectra, refractive index, asterism, and dichroism.

See the article titled The Optical Properties of Minerals for additional information.

Specific Gravity

The weight ratio of a mineral as compared to water. The heaviness of a mineral has to do to the density of it atomical arrangement and the combination of the elements it contains.

See Specific Gravity in Mineral Properties for more information.

Vickers Hardness

The Vickers hardness test is a test performed to measure the hardness of materials, specifically thin sections and small parts. It is comprised of a diamond indenter and a light load to produce an indentation on the subject under testing. The depth of indentation is converted into the hardness value of the object.