Vickers indentation tests of natural quartz were performed with a load of 98 mN at room temperature and one atmosphere. Atomic force microscopy revealed no evidence of fracturing during indentation. Transmission electron microscope observations indicate that no dislocations were generated during the indentation tests. However, high resolution electron microscopy revealed that sharp creases of crystal lattices had developed. These observations lead to the conclusion that quartz deformed plastically even at room temperature. The plastic strain was accommodated by the mechanism of lattice creasing, which is described here for the first time. ¿ 2000 American Geophysical Union