A grinding apparatus for thoroughly crushing, particulating and/or fragmenting materials that are firm or soft. The apparatus is particularly suitable for grinding plant leaf tissue. The grinding apparatus includes a rotatable reamer and a cup for receiving the reamer. The reamer has teeth that form a grinding surface, these teeth extending radially outward from a center point of the grinding surface. A second set of teeth form the inner bottom surface of the cup and provide another grinding surface. The cup teeth correspond to the reamer teeth so as to mesh therewith and produce a camming action during rotation of the reamer.