saprolite

noun Petrography.

1. soft, disintegrated, usually more or less decomposed rock remaining in its original place.

noun

1. a deposit of earth, clay, silt, etc, formed by decomposition of rocks that has remained in its original site

1. Soft, thoroughly decomposed and porous rock, often rich in clay, formed by the in-place chemical weathering of igneous, metamorphic, or sedimentary rocks. Saprolite is especially common in humid and tropical climates. It is usually reddish brown or grayish white and contains those structures (such as cross-stratification) that were present in the original rock from which it formed.