Minerals can be identified by examining their many features. The most useful of these are streak, colour, optical properties, density, hardness, cleavage, crystalline form and chemical properties. In this way, over 4,200 different minerals have been discovered and categorised in 10 different chemical groups.
Colour and streak colour
The colour of a mineral may vary from one sample to another, but the streak colour will not. The streak colour can also be very different from the colour of the mineral itself.
Lustre
Lustre can take many forms. Here are examples of a metallic lustre and a silky lustre.
Density
To measure its density, a mineral must be weighed twice: once dry and once hanging in water. The ratio between the two measurements tells us its density.
Cleavage or fracture
Every mineral has its own distinctive way of breaking. Measuring the angles between the planes makes it easier to identify the mineral.
Hardness
Mohs’ scale can be used to compare the hardness of one mineral with that of others. You just need to see which mineral will scratch the other.
Crystal shape and crystal structure
Every mineral has its own shape. This is determined by the arrangement of the atoms within the crystals. Shape and crystal structure are important features for the exact identification of minerals.