October has two birthstones: opal and tourmaline. Tourmaline is available in many different colors and can have several colors in one stone. Opals are formed from non-crystalline silica gel that hardens into crystals that create different color patterns.
As a birthstone, opal represents peace, harmony and purity. Different types of opals include black, fire, milk and crystal opals. Within each gem are particles of different radiant colors such as green, yellow and blue, that are unique to each stone.
A popular variety of tourmaline is called watermelon tourmaline. This gem version is cut so that the stone has a pink center, a white ring and an outer green edge.