Gems have refractive index, dispersion, specific gravity, hardness, cleavage, fracture, and lustre. Emerald (green), aquamarine (blue), bixbite (red), goshenite (colorless), heliodor (yellow), and morganite (pink) are all varieties of the mineral species beryl.
For example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. Gems are classified into different groups, species, and varieties. For example diamonds, which have a cubic crystal system, are often found as octahedrons. Another term used is habit, the form the gem is usually found in. Next, many gems are crystals which are classified by crystal system such as cubic or trigonal or monoclinic. Diamonds for example are made of carbon (C) and rubies of aluminium oxide (Al 2O 3).
First, what is it made of, or its chemical composition. Gemstones are described by gemologists using technical specifications.