On a standard diamond tester, which simulant can cause it to indicate diamond?

• A. Cubic zirconia
• B. Synthetic moissanite
• C. Glass
• D. Natural diamond

Answer: (B)

Diamond testers work by measuring how quickly a stone conducts heat. Diamond is an excellent heat conductor, so the tester expects a rapid dissipation of heat and indicates “diamond” when the reading crosses its threshold. Synthetic moissanite, made from silicon carbide, has very high thermal conductivity—closer to diamond than many other simulants—so some testers can interpret its heat flow as diamond. That means moissanite can fool a standard tester into signaling diamond even though it isn’t. Glass and cubic zirconia have noticeably lower thermal conductivity, so they generally won’t trigger a diamond reading. Natural diamond will consistently test as diamond.