Definitions

Acicular mineral:

A mineral that grows in long, slender, needle-like crystals.

Cleavage:

The tendency of some minerals to split along smooth surfaces in definite directions.

Conchoidal fracture:

A type of fracture having long, curved surfaces, like the inside of a shell.

Crystal:

Crystals are solid bodies bounded by smooth surfaces called faces, that meet in definite angles. The internal structure--the arrangement of its molecules--determines the crystal's faces and angles.

Fluorescence:

A form of luminous energy emitted when certain minerals are irradiated with ultraviolet light.

Fracture:

The way in which a rock or mineral breaks.

Heavy minerals:

Minerals with a specific gravity greater than 2.87.

Luminescence:

An emission of light due to a stimulus like directed pressure, heating, rubbing, irradiation with X-rays, ultraviolet light, etc.

Lustre:

The manner in which light is reflected from a rock or mineral's surface.

Mohs Scale:

A relative scale of the hardness of minerals, arbitrarily reading from 1 to 10.

Native Elements:

Native elements are uncombined with other elements. Native metals are found as minerals, such as gold, silver and copper.

Ore:

A large enough deposit of one type of mineral to warrant its recovery and extraction for profit.

Plumose:

A mineral with a compact mass and slender branching crystals similar to feathers. This structure is common to some sulphosalt minerals.

Pycnometer:

An instrument for measuring the specific gravity of a mineral or rock.

Radioactivity:

Spontaneous disintegration of the atomic nucleus of some chemical elements with the emission of energetic and charged particles (alpha, beta and gamma rays).

Secondary minerals:

Minerals formed by change at the loss of pre-existing minerals.

Sectile:

A soft mineral that will produce a thin shaving when cut by a knife.

Specific Gravity:

The density (mass/volume) of a mineral relative to the density of water.

Streak:

The colour of the line when a mineral is rubbed against a piece of unglazed porcelain; a mineral in powder form.

Striation:

Parallel lines that define the edges of twinned crystals where the twinning process is repeated; or the result from a conflict between two unique crystal faces with different growth rates.

Transparency:

A mineral is transparent if you can see clearly through it. If light can pass through without showing shapes at all, the mineral is translucent. One that lets no light pass through is opaque.

Twin:

Two or more crystals intergrown with a distinct relationship between crystal structures, so the face of one crystal is parallel to an unlike face of another.