Density

Density, also called specific gravity, describes the ratio between an object's mass and its volume (ρ = m/V). The density of a mineral also depends on its chemical composition. Elements with a larger atomic mass, such as lead, gold, or barium, result in minerals with a higher specific gravity. Precise density calculations can be performed using X-ray diffractometry. For this, the lattice constants of the crystal structure are measured to determine the volume of the unit cell. Then, the molar masses of the atoms in a unit cell are divided by this volume to obtain the mineral's density.

The density of a mineral is very difficult to determine accurately using simple methods. One possibility is density determination via hydrostatic weighing. For this, however, the mineral sample must consist of a single, dense mineral without pores or cavities. The mineral is then weighed dry. The weight, in grams, is recorded. To measure the volume, a measuring cup is filled with water, and the scale is tared. The sample is then suspended in the water by a thin string. Care must be taken to ensure that the sample does not touch the bottom or the rim. Since water has a density of 1 g/cm³, the weight of the displaced water in grams corresponds exactly to the volume of the submerged stone in cm³. Since we have already weighed the dry stone and now know its volume, we divide the weight by the volume. The result is the density in g/cm³. In our mineral classification system, we have divided all minerals into four categories for rough estimation purposes:

Light (< 2 g/cm ³ )
Normal (2 – 3.5 g/cm ³ )
Heavy (3.6 – 6 g/cm ³ )
Very heavy (> 6 g/cm ³ )

This should allow at least normal and very heavy minerals to be roughly estimated by hand.