A process for forming a strong, low-density proppant, which process includes heating pumice particulates, or shaped agglomerates thereof, so as to form heat-treated pumice particulates, or heat-treated, shaped pumice agglomerates, having an apparent density of 2.4 or less and a crush resistance of no more than 10% fines at 4000 psi. Proppants, and well treatment fluids comprising proppants, meeting these characteristics and processes for treating subterranean formations using fluids which include such proppants are also described.