A particle mixture useful for estimating the locations of rock fractures in rock includes a mixture of particles of proppant with particles of an energetic material having a size, shape, and density that are about the same as for the particles of proppant. Particles of proppant and of an energetic material having the same desired sizes and shapes of the proppant may be obtained by collecting those particles that pass through a sieve of a chosen size but not through a sieve of the next smaller size. The location of rock fractures that contain proppant can be estimated by sending the particle mixture into fractured rock, allowing the energetic particles to release their energy, and afterward estimating the locations in the rock where the energy was released from the particles, thereby providing the locations of fractures in the rock that contain proppant.
STATEMENT REGARDING FEDERAL RIGHTS
 This invention was made with government support under Contract No. DE-AC52-06NA25396 awarded by the U.S. Department of Energy. The government has certain rights in the invention.