Don't let the name fool you. Since ancient times, zircon has been worn and prized as a natural, stunning, and underappreciated gemstone. Cubic zirconia isn't it. Although zircons are available in a variety of hues, blue is the most valuable. These days, blue zircon is a birthstone for December. The color of blue zircon is faint but intense. To enhance its look, the majority of blue zircon has undergone heat treatment.