Zircons have two wildly different uses. The first is as an opacifier in ceramics, in which the hard, heat-resistant mineral is used to make glazes opaque. That industrial use contrasts with their appeal to fine jewelers, who fashion clear, green, or golden-brown zircons into brilliant, cushion, and baguette cut crystals. Zircons can be heated to turn dull, brown stones blue, although some colors produced by heat treatment are not stable and...Continue Reading