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, blue, or golden-brown zircons into brilliant, cushion, and baguette cut crystals. Zircons can be heat-treated to turn brown stones blue or clear, although some colors produced by heat treatment are not...Continue Reading