When testing for imitation or fake diamonds, the double-facet test is used extensively to test for moissanite. If there are doubled facets or a doubled reflection when you look at the diamond through a magnifier, it is probably moissanite. Real diamonds refract light in a single direction, so it's facets appear as single lines.

For best effect, tilt the stone and look at it from an angle to see the doubling effect.

Don't care if it's fake? Modern-day fake diamonds such as cubic zirconia (CZ) or moissanite are hard to tell from the real thing and can offer good value. Check out the links below if you're interested in buying fake diamonds: