Abstract: A mechanical seal for pumps utilized in harsh environments such as coal/oil slurries or the like, where an annular head assembly is disposed in an annular recess in the pump housing, through which a rotatable shaft is journalled. A rotor, biased by a spring which is secured to the shaft, is pressed against the annular head assembly portion of the seal. Each component has a non-planar surface which is in rubbing contact with the another, the non-planar surfaces preferably being the shape of a truncated cone, the juncture of the surfaces being disposed within the space defined by the annular recess, to minimize particulate buildup, the non-planar faces permitting self-seating thereof due to misalignment, wear or contamination.