A sensor comprising three electrodes forming two electrode pairs, each pair having a gap between the electrodes, is disclosed. An electrically insulating layer is disposed in the gap of one electrode pair. The sensor may include a RC oscillator circuit connected to the electrode pair having the insulating layer such that the electrode pair contributes to the capacitance of the circuit. The sensor may include a power supply connected to the other electrode pair to provide a voltage across and current through material in the pair's gap. The sensor may be disposed in a borehole to allow borehole fluid to enter the gaps and the RC oscillator circuit and power supply may be operated to provide a measure of capacitance and resistance characteristics of the borehole fluid.