lithofacies

This term is used exclusively within the specialized register of geology and sedimentology. It describes the specific physical and chemical properties of a rock layer, such as grain size, mineral composition, and bedding structures, which allow scientists to reconstruct the environment where the sediment was originally deposited.

Grammatically, this word is an invariant noun. It possesses the same form in both its singular and plural applications, meaning it does not take an "s" or any other suffix to indicate plurality. Whether referring to a single set of characteristics or multiple distinct types, the word remains "lithofacies."