A method, system and apparatus for testing properties of a rock formation surrounding a wellbore in situ. The apparatus includes a tool body, one or more indenters, and one or more acoustic sensors. The body includes an outer surface that defines one or more cavities therein. Each cavity extends into the body. Each indenter is positioned within a corresponding cavity and is positionable into an operating position and a non-operating position. The acoustic sensor is positioned within the cavity and adjacent to the indenter. The indenter is positioned at least partially beyond the outer surface when in the operating position. The acoustic sensor senses one or more acoustic events occurring when the indenter is in the operating position. The apparatus is inserted into the wellbore. Once inserted, the indenter applies a load onto the rock formation causing cracking and the sensor receives the generated acoustic transmissions. The transmissions are analyzed.