Abstract: A microelectric method and apparatus for recording and differentiating between open and closed fractures along the walls of boreholes is disclosed. A main current and a controlled opposing or bucking current are fed into a hard rock formation in a measurement area of a borehole wall insulated from the drilling mud in the borehole. Within this measurement area absolute potential and potential differences are measured and dimensionless ratios based on the measurements of current and potential are ascertained. The ratios indicate the presence of fractures and allow differentiation between open and closed fractures allowing determination of an open fracture network. The apparatus is made up of at least one measuring pad (6) made of insulating material forced onto the wall of borehole.