A gem species is a mineral with one chemical composition and one crystal structure, such as corundum, beryl or quartz.
In more detail
The species sets the optical and physical properties: refractive index, hardness and specific gravity. Ruby and blue sapphire share the refractive indices of corundum, but not their color. A species can have many varieties.
On a grading report
Report layouts differ. Some labs print the mineral as 'Identification' and the variety name, such as ruby, under 'Species'.
Related terms
- Gem variety: A variety is a subdivision of a gem species, usually by color. Ruby and sapphire are varieties of corundum, and emerald is a variety of beryl.
- Corundum: Corundum is the mineral species made only of aluminum and oxygen. Its red variety is ruby, and all its other colors are sapphire.
- Beryl: Beryl is the mineral species of emerald. Aquamarine and the other beryl colors belong to the same species.
- Quartz: Quartz is the mineral species of amethyst and citrine. It is silicon dioxide in a trigonal crystal.
- Crystal system: A crystal system groups crystals by the symmetry of their atomic structure. Gemologists use seven: cubic, tetragonal, hexagonal, trigonal, orthorhombic, monoclinic and triclinic.