Ruby is the most valuable type of the Corundum minerals which also include Sapphire. A good Ruby is easily more valuable than a Diamond and they command the highest price per carat of any other colored gemstone. Which makes Ruby one of the most important gems. In its pure form Corundum is clear however trace elements of other minerals provide the rich colors these gems are famous for. In the case of Ruby Chromium is what gives Rubies their rich red colors.
Ruby is the birthstone for July.
refractive index: 1.762 to 1.770
Specific Gravity: 4.00
MOHS Hardness: 9