Ruby

Ruby was a variety of corundum that was a popular and plentiful jewel and had many magical uses in addition to its appeal as a sparkling gemstone.

Description
Rubies came in a variety of colors, from colorless through shades of red to deep crimson. The darker the shade and the fewer the inclusions and impurities, the more valuable was the gem. A typical specimen had a base value of 5,000 gp. About one in every hundred rubies was a star ruby.

Powers
Superstitions around the Sea of Fallen Stars held that rubies bestowed good luck on their owners, but magical uses were much more reliable. Crushed to a powder and used in the enchantment, rubies greatly enhanced personal magic items that increased skill, ability, resistance, or luck. Ruby powder was also used to create the magic ink for scribing divine spells of the elemental and sun spheres, and arcane spells of the abjuration, alteration, or evocation schools. The best time of day to use powdered ruby was "the time of the summer sunset."

Facet cut and polished rubies were required in the crafting of a helm of brilliance and were the gem of choice in decorating items that produced healing magic. With the proper incantations, rubies could ward against natural and magical lightning and earthquakes. Extremely rarely, a ruby might contain a creature that could be released from the stone by delicately shattering it. Such creatures were usually unknown in Faerûn and grew rapidly upon release.