Both the oceanic and continental crusts are partly covered with a thin layer of sedimentary rocks and sediments. These consist mainly of clastic rocks such as sandstone, siltstone and shale, along with carbonate rocks such as dolostone and limestone. These clastic rocks are composed of mainly quartz, clay minerals, and a small amount of micas and feldspar minerals. The carbonate rocks consist primarily of calcite and dolomite. A small number of materials, composed of a small number of minerals, make up most of the sediment and sedimentary rocks that cover the continents and ocean basins.