Why measure the specific gravity of a mineral?
Because specific gravity is one of the most important, constant, and quantifiable properties of a gem or mineral, and in your effort to identify an unknown stone, the specific gravity, if known, can narrow down your search to just a handful of possibilities. The specific gravity for each mineral is the same within narrow limits (except in species like topaz or garnet and zircon where subgroups with definite specific gravities occur). Must my mineral specimen be pure? Yes and No. No, because you can theoretically measure the specific gravity of any solid using these devices, whether it be a chunk of plastic, a rock containing a varying amount of minerals, or a pure mineral itself in the form of a crystal. But yes, your mineral specimen must be pure if you wish to compare your measurement to standards of specific gravity for those minerals, which standards were developed using pure mineral specimens. In summary, the more pure your specimen, the more accurate will be your specific gravity
