Fine Alexandrites exhibit a color change from green in daylight to red in artificial light, and are extremely expensive. These days, most people either choose to use the Pearl, a small affordable Alexandrite, or to use a beautiful synthetic color-change sapphire which mimics the qualities of Alexandrite at a fraction of the cost. Extreme care should be taken wearing Alexandrites, to protect them from temperature extremes and sharp impacts. So much so, that soldiers believed that carrying one made them invincible. Rubies were also associated with mythical creatures like the Dragon.
Rubies are the mineral corundum, which is second only to Diamond in hardness.
Corundum, by the way, is also known as sapphire. A red corundum is called a Ruby, while a pinkish color and all other colors are called Sapphire. Once thought to bring happiness in marriage and the power of eloquence in speech, other cultures believed that it had the power to cure asthma and fend off a fever's thirst. Peridots range in color from a beautiful light yellow-green to an intense grass green to a deep olive green. Often the more porous light brown layer is dyed dark brown or black, while the white resists the color, making for a more striking cameo or intaglio.