Abstract: It has been learned that moissanite and other synthetic stones, including synthetic moissanite and synthetic diamond, are distinguishable from natural diamonds based on differing electrical conductivities. The present invention, therefore, provides an apparatus and method for determining a gem type based on its electrical conductivity. In particular, an electronic circuit including the gem under test as part of a circuit path is used to measure its electrical conductivity and, therefore, gem type. The onerous task of determining whether a gem is moissanite or synthetic diamond involves providing a high voltage across a gem surface greater than a breakdown voltage, typically greater than 300 volts, and measuring a minuscule current that flows through the gem. A first and second contact couple the high voltage to the gem under test, where a low impedance detection circuit is used to flag when the contacts are erroneously contacting each other during a measurement.