A rock ripping tool mountable to an excavation machine for engagement with a substrate has a rotatable tool body, a pair of side plates and a curved back plate mounted to the body, a bottom plate with an angled leading edge mounted to span a space between side plates, and a plurality of teeth, including a first set mounted to the front edge, the tip of each tooth lying on an arc having a first radius, a second set mounted to the bottom and/or back plate, the tip of each tooth lying an arc having a second radius greater than the first radius, and a third set of teeth mounted to the bottom plate and/or the back plate, with the tip of each tooth lying on an arc having a third radius greater than the first and second radii. Each tooth is configured to engage the substrate sequentially and individually.