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We have measured the density and determined the porosity of 198 samples of ash flow tuffs from three boreholes at Yucca Mountain, Nevada. The electrical properties, velocity, and permeability of many of these samples have also been determined. We use mineralogical and physical data from other sources to determine the dependence of measured physical properties upon petrology. Porosity in the samples varies over a wide range, from as low as 1% in the densely welded tuffs to 53% in the zeolitized nonwelded tuffs. Porosity is the primary control on the other measured physical properties that consequently vary over broad ranges. Alteration (zeolites and clays) is a primary control on grain density and a significant secondary control on bulk density, resistivity, velocity, and permeability. Sorting the samples into rock classes defined in terms of the degree of welding and gross mineralogy enables us to separate the influence of zeolites and clays from that of porosity. Empirical rock property relationships established for sandstones can be applied with good success to tuffs. Archie's law relating resistivity to porosity is found to fit the unaltered samples with an exponent m of 2.0. An empirical expression relating compressional velocity to porosity and clay content forms an excellent upper bound to the velocity-porosity data. Permeability-porosity plots are similar in form to those obtained for clastic rocks, although the permeability is considerably lower than in clastic rocks of similar porosity. Zeolites and clays reduce the grain density, increase the electrical conductivity, reduce the compressional velocity, and reduce the permeability.