The specific gravity is a measure of whether a mineral is heavy or
light. It is a comparison of the weight of a piece of the mineral with
the weight of an equal volume of water. The mineral quartz, for example,
has a specific gravity of 2.65. This means that a piece of quartz is a
little more than 2½ times as heavy as an equal volume of water. Accurate
measurements of specific gravity can be made in a laboratory. You can,
however, learn to estimate specific gravities just by lifting various
minerals and judging whether they are heavy or light.