What simple test is commonly used to differentiate most diamonds from many simulants in the field?

• A. Visual inspection with a loupe
• B. Visual inspection with magnification and basic hardness test
• C. Thermal conductivity test alone
• D. A combination of thermal conductivity testing and refractive index testing

Answer: (D)

In the field, distinguishing diamonds from simulants is most reliable when you combine tests for thermal conductivity and refractive index. Diamond’s ability to conduct heat well is a telltale sign, but some simulants, especially moissanite, can mimic that property, so a single test isn’t definitive. A refractive index test adds a second, independent clue: diamonds have a refractive index around 2.42, while common substitutes differ (moissanite is higher, roughly 2.65, and cubic zirconia is lower, around 2.15). Using both tests together lets you cross-check heat behavior with light-bending, reducing misidentification. In practice, you’d start with a quick thermal conductivity check and, if it suggests possible diamond, confirm with a refractive index assessment to rule out high-conductivity simulants or index-mifferent stones. Visual inspection alone isn’t reliable, and relying on a single property can be fooled by certain simulants, so the dual-criterion approach is the most robust field method.