October's birthstones are opal and tourmaline.
Opal is a hardened silica gel that contains 5 to 10 percent water. Its opalescence is caused by refracting light off of silica spheres within. Australia, Japan, and the United States are major sources.
Known as the "Queen of Gems," opals have long been a symbol of loyalty and hope.
No other stone has the rich color variations of tourmaline. It occurs in many hues, including pink, green, violet, blue, and black. Pink-to-red crystals with a green edge, or "rind" are called Watermelon, a reference to their similarity to the fruit.
Today it is thought to be a powerful healer. Its primary sources are Sri Lanka and Brazil.