Compositions and methods for determining the origin location of subterranean rock samples. In some implementations, the compositions include a nanoparticle tag that includes a natural polysaccharide, a fluorescent dye, and superparamagnetic nanoparticles. In some implementations, a method of determining the origin location of a subterranean rock sample includes mixing the nanoparticle tag into a fluid, flowing the fluid into a subterranean formation, recovering subterranean rock samples from the formation, separating tagged rock samples from untagged rock samples using a magnet, and determining the origin location by analyzing a fluorescent signal of the nanoparticle tag.