sentence: Basaltic tuffs are black, dark green or red in colour.
sentences_after: They vary greatly in coarseness. Often submarine, they may contain shale, sandstone, grit and other sedimentary material, and are occasionally fossiliferous. Recent basaltic tuffs are found in Iceland, the Faroe Islands, Jan Mayen, Sicily, Sandwich Islands, Samoa, etc.
concept_name: basaltic tuff
headings: Tuff Basaltic tuffs
categories: Igneous rocks