A _natural gemstone_ is a mineral, stone, or organic matter that can be
cut and polished or otherwise treated for use as jewelry or other
ornament. A precious gemstone has beauty, durability, and rarity,
whereas a semiprecious gemstone has only one or two of these qualities.
A _gem_ is a gemstone that has been cut and polished.
Diamond, corundum (ruby and sapphire), beryl (emerald and aquamarine),
topaz, and opal are generally classed as precious stones. All other
gemstones are usually classed as semiprecious.
A _mineral_ is any naturally formed homogeneous inorganic material.
A _mineralogist_ is a person who studies the formation, occurrence,
properties, composition, and classification of minerals.
A _gemologist_ is a person who has successfully completed recognized
courses in gemology (the science and study of gemstones) and has proven
skills in identifying and evaluating gem materials.
A _lapidary_ is a cutter, polisher, or engraver of precious stones.