Saprolite is the heavily degraded remains of bedrock. It is formed by the decomposition of regoliths that have remained in their original site, but have been affected by chemical weathering to the point where they are notably more fragile and porous. Saprolites may appear as a dense deposit of earth, clay, or silt, or a more robust but still weakened form of the parent rock. They will generally maintain the original structures, such as stratification or cross-bedding, that were present in the original rock from which they formed.
Saprolite usually forms in tropical and temperate climates and in areas of high rainfall, resulting in higher rates of chemical leaching and dispersion. Even in these conditions regoliths take millions of years to degrade; while saprolite can form in cooler, drier climates, it would take a much longer time.
Any parent material containing significant amounts of unstable or soluble minerals can degrade into saprolite; this includes the sulfide minerals, carbonate minerals, and minerals of the Serpentine group. Closely related rocks include laterite, kaolinite (saprolites containing aluminum and silicon; often called kaolin or china clay), and goethite (one form of iron rich saprolite). Saprolite may also be appended to a description of an existing rock; for example 'saprolitic granite' (AKA rotten granite) or 'diorite saprolite'.
Saprolite comes from the Greek sapros, meaning putrid, and lithos, meaning stone. Hence, saprolite literally means rotten rock.