A Stone is a mineral, rock (as in lapis lazuli) or petrified material that when cut or faceted and polished is collectible or can be used in jewelry. Others are organic, such as amber (fossilised tree resin) and jet (a form of coal). Some beautiful Stones are too soft or too fragile to be used in jewelry.

Stones are classified into different groups, species and varieties. For example, ruby Stone is the red variety of the species corundum that belongs to the spinel or hematite group. Emerald (green), aquamarine (blue), bixbite (red), goshenite (colorless), heliodor (yellow), and morganite (pink) are all varieties of the mineral species beryl.

Stones have refractive index, dispersion, specific gravity, hardness, cleavage, fracture and luster. Stone may exhibit pleochroism or double refraction. Stone may have luminescence and a distinctive absorption spectrum.

A Stone is prized especially for great beauty or perfection so appearance is almost the most important attribute of Stones. Characteristics that make a Stone beautiful or desirable are colour, unusual optical phenomena within the Stone, an interesting inclusion such as a fossil, rarity, and sometimes the form of the natural crystal.

Diamond is prized highly as a Stone since it is the hardest substance known and is able to reflect light with fire and sparkle when faceted.