composed primarily of mineral material solid layer mineral horizon 2021-02-02T21:33:40.901Z A soil horizon which is primarily composed of mineral material. ADDED 'composed primarily of' RO:0002473 mineral material 'ENVO:01000256' Usually less than 20% organic carbon. The term mineral horizon refers to surface soil/topsoil and subsoil layer of the soil. When user does not/could not refer to the topsoil or subsoil specifically, the broader term, mineral horizon can be used. soil horizon