IDENTIFICATION OF MINERALS

How can a Mineral be Identified

Each mineral has a definite chemical composition and crystalline structure.

These two characteristics are the fingerprint of the mineral

Various chemical tests in laboratories can be done on a mineral to determine its composition.

X-ray diffraction can be used to determine its crystalline structure.

The procedures in the laboratories are time consuming and costly.

Of the 4000 minerals, only 20 are common, so identification becomes easier, as they can be determined for the most part by their physical characteristics.

The process still take practice and good observation skills

Physical Properties for Identification of Minerals

Colour Streak Crystal habit Hardness Cleavage Fracture Lustre Specific gravity

Colour The most obvious, but least reliable. Many minerals can be found in different

colours. Example is Quartz – white, clear, purple,

brown, pink, and black

Streak This test is very reliable. Streak is the colour of the mineral in

powder form. The colour is found by scratching the

mineral against a piece of porcelain (called a streak plate).

External Crystal Habit The shape that we see of the mineral

maybe a clue. Some common crystal habits are:

A crystal is an external expression of a mineral’s internal arrangement of atoms. All minerals have an orderly internal arrangement of atoms, but crystals are rarely observed in nature.

Minerals do not always form there natural characteristic because they are competing for space when they are growing. Therefore they need room to grow.

This means the mineral must either have the strength to grow in a space, or have an environment that allows for growth.

Hardness This is the minerals resistance to

scratching. The degree of hardness is indicated with

a number on the Moh’s Hardness Scale

Cleavage Cleavage is the tendency of some minerals, when

struck to break along distinct planes. These planes represent areas of weak bonding in the

mineral’s crystal structure.

A mineral may cleave; In one plane Two planes at 90º Two planes at angles other than 90º Three planes at 90º Three planes at angles other than 90º

Or a mineral may not cleave, which is called fracture

Lustre The lustre of a mineral is the way its surface reflects

light. Most terms used to describe lustre are self-explanatory:

metallic, earthy, waxy, greasy, vitreous (glassy), adamantine (or brilliant, as in a faceted diamond).

It will be necessary, at least at first, only to distinguish between minerals with a metallic lustre and those with one of the non-metallic lustres.

A metallic lustre is a shiny, opaque appearance similar to a bright chrome bumper on an automobile.

Other shiny, but somewhat translucent or transparent lustres (glassy, adamantine), along with dull, earthy, waxy, and resinous lustres, are grouped as non-metallic.

Specific Gravity The specific gravity of a substance is a comparison of

its density to that of water. Specific gravity can be measured precisely, or

estimated by a comparison. To compare the specific gravity of any two minerals,

simply hold a sample of one in your hand and "heft it," i.e., get a feeling for its weight.

Then heft a sample of the other that is approximately the same size.

If there is a great difference in specific gravity, you will detect it easily. It is often sufficient to note whether a mineral's specific gravity is significantly higher or lower than that of other minerals.

These physical characteristics should be used in combination to identify a mineral.

A Mineral Identification Key is a good tool to use when start out with the identification of minerals