# What is specific gravity in mineralogy ?

## Specific gravity : definition

Specific gravity (usual) is the quotient of the mass of a body by the mass of the same volume of pure water at 4 °C. Specific gravity is therefore a dimensionless number.

In mineralogy, the specific gravity can be appreciated "by hand". With some practice, we can distinguish light minerals (specific gravity less than 2.5), heavy minerals (specific gravity greater than 4), and very heavy minerals (specific gravity greater than 6). The density of the earth's crust being 2.6, minerals with a density close to this figure appear to us to be of "normal" weight.

Specific gravity is a characteristic and important value of minerals which can be easily measured with a pycnometer. We can also calculate the density (ms) expressed in g/cm3, equivalent to the specific gravity, and improperly called calculated density.

It responds to the formula: ms = Z x M / N x V
With:
M : Atomic mass of the mineral
V : Volume of the elementary cell
Z : Number of formulas - units in the mesh