In USDA soil taxonomy, orthents are defined as entisols that lack horizon development due to either steep slopes or parent materials that contain no permanent weatherable minerals (such as ironstone). Typically, Orthents are exceedingly shallow soils. They are often referred to as skeletal soils or, in the FAO soil classification, as lithosols. The basic requirement for recognition of an orthent is that any former soil has been either completely removed or so truncated that the diagnostic horizons typical of all orders other than entisols are absent.