Abstract: A simulated diamond such as crystalline cubic zirconia, which has optical properties very similar to natural diamond and so is difficult to distinguish optically from natural diamond, is distinguished from natural diamond by measuring its thermal conductivity which is significantly different from the thermal conductivity of natural diamond, by measuring the temperature of a heated probe held against the simulated diamond as an indication of the simulated diamond thermal conductivity. In a preferred embodiment of the present invention, a controlled amount of heat energy is generated at the probe and thereafter, while the probe is held against the simulated diamond, the temperature of the probe is detected as a measure of relative thermal conductivity of the simulated diamond to the natural diamond.

Abstract: A simulated diamond such as crystalline cubic zirconia, which has optical properties very similar to natural diamond and so is difficult to distinguish optically from natural diamond, is distinguished from natural diamond by measuring its thermal conductivity which is significantly different from the thermal conductivity of natural diamond, by measuring the temperature of a heated probe held against the simulated diamond as an indication of the simulated diamond thermal conductivity. In a preferred embodiment of the present invention, a controlled amount of heat energy is generated at the probe and thereafter, while the probe is held against the simulated diamond, the temperature of the probe is detected as a measure of relative thermal conductivity of the simulated diamond to the natural diamond.

Abstract: Natural diamonds can be distinguished from simulated diamonds in seconds by merely touching a hand held probe to the gems. The tip of the probe includes a rounded gem contacting head of high thermal conductivity and low thermal mass. The head is preferably of gold-coated copper. It is supported on a high thermal resistivity neck extending from a large spring biased thermal mass. The head supports a thermistor heater element and a thermistor temperature sensing element within an annular space. Pulses of power are cyclically applied to the heater element to produce a predetermined amount of heat flow from the probe through the sample gem. The resulting change in temperature of the contacting head is determined by sensing the change in resistance of the sensing thermistor and weighting that change by the sensed thermistor resistance. The weighting function is carried out by a gain-controlled amplifier.