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.
Amethyst crystals, Mexico
Photograph courtesty of
The Smithsonian Institution
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.