A shear retort mill for slow ablative pyrolysis features friction heating between shearing surfaces on a rotating disk and a static or rotating cylindrical drum enclosing the disk. A feed enters the workspace between the rotating disk and the bottom of the drum through a hollow feed shaft coupled to the rotating disk. Preferably, an auger compacts and moves the feed downward, and a shredder reduces the feed's particle size. The feed is increasingly ground and pyrolyzed as it is forced between the drum and disk shearing surface. As the dense processed material extrudes at the edge of the workspace, the gases and liquid products are forced inward by the barrier of dense solids. A static exhaust pipe at the center of the rotating feed shaft allows for the exit of these gases, which preferably go to a heat exchanger to recover any condensable fractions.