Abstract: The present invention embodies an improved method for the in situ mining of low to impermeable minerals to sweep out sections of deposits beneath the surface of the earth.

Abstract: Hollow, fine-grained ceramic proppants are less expensive and improve fracture control when compared to conventional proppants (dense alumina, mullite, bauxite, zirconia, etc.). Hollow proppants of the present invention have been fabricated by spray drying, followed by sintering in order to obtain a dense case and a hollow core. These proppants generally have high sphericity and roundness (Krumbein sphericity and roundness greater than 0.8), have diameters on average between 2250 and 125 .mu.m, depending on proppant size required, and have strength equal to or greater than that of sand. The hollow core, the size of which can be controlled, permits better fracture control in hydraulic fracturing treatments since the proppant can be transported in lower viscosity fluids. Hollow proppants produced at the same cost/weight as conventional proppants also provide for lower costs, since less weight is required to fill the same volume. The fine-grained (preferably less than 5 .mu.

Abstract: The present invention relates to a method for measuring the fracture toughness of rock as it would exhibit in its natural down-hole setting. Practicing the method of the present invention involves internally pressurizing a rock specimen while simultaneously exerting an increasing external horizontal stress thereon, raising simultaneously the internal pressure to maintain a desired relationship of exterior to interior pressures until the specimen fractures, which pressure, in relationship to the stress intensity factor and specimen geometry, provides the specimen fracture toughness as it would exist in a down-hole situation.