Authigenic quartz euhedra are described from a well drilled in the Lockport Formation (Middle Silurian) southwestern Cattaraugus county, southwestern New York State. The formation is dolostone part of which is dolomicrite; the latter, occurring in the top-half of the formation, is the host to authigenic quartz euhedra which occur isolated or in aggregates. Isolated euhedra are equant, prismatic, or lath shaped and display extensive boundary corrosion and length-slow optical character. Aggregates of quartz euhedra are either fan-shaped or clusters composed of euhedra radiating out in all directions. In both cases corrosion effects and length-slow optical character are seen. These authigenic quartz euhedra are interpreted as filling voids created by dissolution of sulfate crystals. Features leading to this interpretation are quartz crystal morphology, comparison of quartz euhedra with detrital quartz, and comparative crystal morphology of quartz and sulfates (gypsum and celestite). Precipitation of sulfates must have occurred in lime mud which contained detrital quartz. The pH fluctuations led to sulfate dissolution and quartz precipitation. Finally, dolomitization resulted in corrosion of quartz-crystal boundaries.