Zircon ranges from 6 to 7.5 on the Mohs scale of hardness. It is commonly heat treated to produce blue and colorless varieties, as well as orange, yellow and red. The gem is generally stable when exposed to light, but some heat-treated stones may revert to their original colors (usually light brown) after prolonged exposure to bright light. Exposure to heat can alter the color of some zircon. This December birthstone is stable when exposed to chemicals. Because zircon tends to abrade, it is best to avoid wearing it in rough conditions, such as while gardening, playing sports or doing dishes. Clean your zircon using a soft brush and mild soap in warm water. Ultrasonic and steam cleaners are not recommended for this December birthstone. How is Zircon Generally cut? Colored stones get a brilliant or step (emerald) cut. Usually, round gems earn a "zircon" cut which is similar to a standard round brilliant cut with an extra row of facets at the edges and these gems really sparkle. Bling Runway also supplies many oval shaped Zircon Gemstones as well.