An electric instrument for testing the piezoelectric properties of crystalline powders is described. The instrument consists of a rf oscillator, frequency modulated at the rate of 150 Hz with deviation of about 2 kHz. The sample is contained in a capacitor of the oscillator tuning circuit. The oscillator frequency is slowly and continuously shifted in a wide range of frequencies. When one of the resonant frequencies of the microcrystal powder belongs to the range of frequencies swept by the oscillator, the sudden fall of the impedance of the tank circuit appears as an amplitude modulation of the rf carrier. This modulation signal detects the piezoelectricity of the sample.