A basic diamond tester tests the thermal conductivity, which measures the rate at which heat is transferred through a gemstone. Diamonds are known for their high thermal conductivity, which is one of their unique properties. Similarly, moissanite also has high thermal conductivity. That is why it passes as a diamond in testers like these. Moissanite has a lot more similarities to diamonds such as hardness and appearance. One striking difference is the affordability. So with moissanite, you have