<P> This fourth miscellaneous category includes rocks formed by Pyroclastic flows, impact breccias, volcanic breccias, and other relatively uncommon processes . </P> <P> Alternatively, sedimentary rocks can be subdivided into compositional groups based on their mineralogy: </P> <Ul> <Li> Siliciclastic sedimentary rocks, are dominantly composed of silicate minerals . The sediment that makes up these rocks was transported as bed load, suspended load, or by sediment gravity flows . Siliciclastic sedimentary rocks are subdivided into conglomerates and breccias, sandstone, and mudrocks . </Li> <Li> Carbonate sedimentary rocks are composed of calcite (rhombohedral CaCO), aragonite (orthorhombic CaCO), dolomite (CaMg (CO)), and other carbonate minerals based on the CO ion . Common examples include limestone and dolostone . </Li> <Li> Evaporite sedimentary rocks are composed of minerals formed from the evaporation of water . The most common evaporite minerals are carbonates (calcite and others based on CO), chlorides (halite and others built on Cl), and sulfates (gypsum and others built on SO). Evaporite rocks commonly include abundant halite (rock salt), gypsum, and anhydrite . </Li> <Li> Organic - rich sedimentary rocks have significant amounts of organic material, generally in excess of 3% total organic carbon . Common examples include coal, oil shale as well as source rocks for oil and natural gas . </Li> <Li> Siliceous sedimentary rocks are almost entirely composed of silica (SiO), typically as chert, opal, chalcedony or other microcrystalline forms . </Li> <Li> Iron - rich sedimentary rocks are composed of> 15% iron; the most common forms are banded iron formations and ironstones . </Li> <Li> Phosphatic sedimentary rocks are composed of phosphate minerals and contain more than 6.5% phosphorus; examples include deposits of phosphate nodules, bone beds, and phosphatic mudrocks . </Li> </Ul> <Li> Siliciclastic sedimentary rocks, are dominantly composed of silicate minerals . The sediment that makes up these rocks was transported as bed load, suspended load, or by sediment gravity flows . Siliciclastic sedimentary rocks are subdivided into conglomerates and breccias, sandstone, and mudrocks . </Li>

What type of sedimentary rock was formed at layer x