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Dry bulk density and grain density measurements were made on 182 samples of igneous, sedimentary, and metamorphic rocks from various world-wide localities. Total porosity values and both water-accessible and heliumaccessible porosities were calculated from the density data. Magnetic susceptibility measurements were made on the solid samples and permeability and streaming potentials were concurrently measured on most samples. Dry bulk densities obtained using two methods of volume determination, namely direct measurement and Archimedes' principle, were nearly equivalent for most samples. Grain densities obtained on powdered samples were typically greater than grain densities obtained on solid samples, but differences were usually small. Sedimentary rocks had the highest percentage of occluded porosity per rock volume whereas metamorphic rocks had the highest percentage of occluded porosity per total porosity. There was no apparent direct relationship between permeability and streaming potential for most samples, although there were indications of such a relationship in the rock group consisting of granites, aplites, and syenites. Most rock types or groups of similar rock types of low permeability had, when averaged, comparable levels of streaming potential per unit of permeability. Three calcite samples had negative streaming potentials. INTRODUCTION Various petrophysical properties were measured on 182 specimens of igneous, sedimentary, and metamorphic rocks from two collections that were obtained from Ward's Natural Science Establishment, Inc; namely a standard reference collection of 100 important rock types of North America, and a universal collection that contains rocks from both American and world-wide localities. Table 1 is a compilation of density, porosity, magnetic susceptibility, hydraulic conductivity (permeability), and streaming potential data for all specimens. Rock names used herein were supplied with the collections by Ward's Natural Science Establishment, Inc. A manual that contains petrographic descriptions of all rocks in the North American collection is available from Ward's (catalogue no. 45 W7217), but no such manual exists for the universal collection. However, the latter collection may be purchased with a matching set of thin sections if detailed petrographic analysis is desired. Thin sections corresponding to each rock of the North American collection are also available from Ward's. SAMPLE MEASUREMENT AND TECHNIQUES OF MEASUREMENTS The rock samples, as received, were hand-sized specimens from which 25.4 x 25.4 mm cylindrical plugs were cut using a diamond core drill. In some cases, where parent samples were too small, the cylinder lengths were, by necessity, less than 25.4 mm. The cylinder ends were faced using diamond tools and the samples were then dried overnight in a vacuum oven. Density measurements were obtained on the cylinders using techniques described by Johnson, 1979. Briefly, the samples were weighed dry (W^) to an accuracy of 0.1 mg, and the bulk volumes (V^) were obtained by calipering the lengths and diameters. The apparent grain volumes of the cylinders (Va ) were determined using helium pycnometry. The samples were next saturated with distilled water and then weighed both in air and submerged but suspended in a water bath (buoyancy method). From these data dry bulk densities, DBD, and DBA, and grain densities, SGH and SGA were calculated as follows: UDU = SGH = DBA = W d V a (w S > vi; fy\ 9 \£) w. d W sp P, SGA= (j-r ) P, (4) d sp where W and W are respectively the saturated weights in air and suspended in water. P is the density of distilled water at room temperature. While DBD is an absolute measurement within experimental error, SGH and SGA should be considered apparent grain densities unless it is known that helium or water filled all rock pores. Samples need not be completely saturated to obtain an accurate measurement of DBA, but saturation must be sufficient so that the sample does not absorb water while being weighed suspended in water. Absolute grain densities (SGG) were obtained by crushing and grinding pieces of the hand samples to a grain size considered sufficient to eliminate all pores. The powders were then weighed and the true grain volumes were obtained by helium pycnometry. SGG was calculated using equation (2). Porosities were calculated from the relation between dry bulk density and grain density. Fractional porosity is, by definition, the ratio of pore volume to the bulk volume of a solid material, but if proper substitutions are made from the equations for bulk density and grain density, fractional porosity ( <J> ) can be expressed as , _ .dry bulk density. ... grain density . Total porosities (TOP) were calculated from DBD and SGG; water-accessible porosities (WAP) were calculated from DBA and SGA; and helium accessible porosities (HAP) were calculated from DBD and SGH. Magnetic susceptibilities were measured using a "Bison bridge", an instrument patterned after a design originally described by Mooney (1952). Subsequently, 121 of the samples were remeasured with a USGS-fabricated magnetic susceptibility system. By then many of the samples used in the original measurements were not available. Those reported susceptibilities that were measured with the Bison bridge are asterisked on table 1. Permeability, the commonly-used expression for hydraulic conductivity, was measured concurrently with streaming potential in a stainless steel flow cell (fig 1). The extreme range of expected permeabilities required the use of differing amounts of driving or pore pressures (P^, P£) to force liquid through the samples. Confining pressures (Pc ) were maintained at least 690 kPa greater than pore pressures, and pore pressures ranged from a few kPa to over 2000 kPa. A capillary tube of known inside diameter was affixed to the downstream side of the flow cell and flow rates through the samples were determined by calculating the volume of water displaced in the tube per unit time (q). Permeabilities (k^), in units of darcies, were calculated from the equation v = SEi kd APA' where V» is the viscosity of the pore fluid, P is net pressure difference through the length of the sample in atmospheres, A is the length, and A the cross-sectional area of the sample. For very permeable samples, downstream water was collected in a cup during a fixed time interval and q was determined using volumes derived from weighing the collected water. Streaming potential measurements were made immediately after measuring permeability using a "closed" system (fig. 2). A 0.001M KC1 solution of distilled water was used for all measurements. In all but a few of the most permeable samples P was maintained at about 3450 kPa and (P, P«) was cycled in increments from 0 to about 2200 kPa. P^ and P£ were continuously monitored on a strip chart while voltages between E, and E« were simultaneously recorded. The electrokinetic coupling coefficient ( A E/ AP) was determined for each sample by performing a linear regression by the method of least squares on discrete data pairs of E and Pj-^ at various p i« For those few samples that had permeabilities of greater than one darcy, streaming potentials were measured using much lower values of PC , P^, and P£. DENSITY AND POROSITY According to Manger (1966) bulk volumes obtained from water displacement measurements (equation 3) may be either too large or too small. If, when weighing a saturated sample in air, a residual film of water remains on the sample surfaces, the value for bulk volume will be too great and the DBA will be too small. On porous samples the surface water film tends to vacate the intergranular apices leaving the near-surface pores free of water which results in bulk volume values that are too small and DBA that are too high. This effect is, of course, increased as pore size increases. 1. "Brand names are cited for purposes of complete description and does not constitute endorsement by the U.S. Geological Survey". If the ratios of DBD to DBA are compared the above effects can be evaluated. Ratios of greater than one indicate excess surface water when weighing saturated samples in air, whereas ratios of less than one indicate depletion of water from near surface pores. For all specimens the DBD/DBA ratios are 1.00 or less. Approximately 100 specimens have DBD/DBA of 0.99, and 25 specimens have DBD/DBA of less than 0.99. A ratio of 0.99 results from a difference between DBD and DBA values of about 0.03 Mg/m which in turn can be caused by either near-surface water depletion or inaccuracies in calipered volume determinations when making DBD measurements. Of the 25 samples having low DBD/DBA, 13 have chipped edges and one was partially dissolved during saturation. These samples are identified with a superscript 1 or 2 preceding the DBD value. The remaining 11 samples (superscript 3 preceding the DBA value) are either porous sandstones, pumice, scoria, or samples having large surface vugs. High porosity alone does not necessarily mean that water-saturation bulk density values will be anomalously high. Several very porous specimens have DBD ratios of 0.99-1.00 which can be attributed to small pore size or irregular pore shapes such as so-called ink well pores that limit surface depletion of water when weighing samples in air. Within experimental error SGH for all samples is equal to or greater than SGA, and SGG is equal to or greater than SGH. These relationships are to be expected because helium will enter a smaller diameter pore than water, and reducing a specimen to powder should eliminate most of the very small pores that may be impermeable to helium. For many samples however, these differences are small. Figure 3 shows a plot of SGA against SGG. Most of the sample points fall along a line having a slope of 1 and passing through the origin. On this line SGA SGG. If SGA and SGG values (table 1) are within 0.030 Mg/m3 of each other then SGA is

Rock property measurements and analysis of selected igneous, sedimentary, and metamorphic rocks from worldwide localities