Volcanogenic Sedimentary Rock

rock that consists of volcanic and sedimentary materials, which can be solid and detrital (occurring as a result of explosive volcanic eruptions) or chemical (dissolved in water). Detrital or pyroclastic material (products of the shattering of liquid lava and solid volcanic or other rock) lays down friable accumulations of clumps, volcanic bombs, lapilli, volcanic sand, and volcanic ash. When it is cemented into the place where it fell or is redeposited, generally pure, most often homogeneous, volcanogenic sedimentary rock (tuff), containing only a small admixture (for example, not more than 10 percent) of sedimentary material, is formed. In cases of greater intermingling, which is also facilitated by more prolonged redeposition of the materials, tuffite and ordinary sedimentary rocks with negligible admixtures of tuff components form. Detrital volcanogenic sedimentary rock is divided according to size into very coarse (with particles larger than 10 mm), coarse (2-10 mm), medium (0.1-2 mm), fine (0.01-0.1 mm), and very fine (smaller than 0.01 mm). It is also divided according to mineral composition, above all according to the composition of the volcanic component. Material from hot springs and liquid products of an eruption form chemogenic volcanogenic sedimentary rock when precipitated in seas or on dry land; examples of this are many jaspers and some iron, manganese, and phosphorite ores.