A variety of the mineral topaz, a silicate mineral composed of aluminum and fluorine. While natural blue topaz exists, it's very rare and typically has a very pale color. The vibrant, deeper blue hues commonly found in jewelry, such as Swiss Blue and London Blue, are a result of heat and irradiation treatments on colorless or pale topaz stones. This process is permanent and stable. With a Mohs hardness of 8, blue topaz is a durable and popular gemstone for everyday wear. It is the birthstone for December and is mined in various locations, including Brazil, Sri Lanka, and Nigeria.