What type of rock is sandstone?

• A. Igneous rock
• B. Metamorphic rock
• C. Sedimentary rock
• D. Limestone

Answer: (C)

Rocks are classified by how they form into igneous, sedimentary, and metamorphic. Sandstone is a sedimentary rock because it forms from the accumulation and lithification of sand-sized grains, most commonly quartz, which are cemented together by minerals such as silica, calcite, or iron oxide. That cementation preserves the grain texture and any layering from its sedimentary origin. This distinguishes it from igneous rocks, which crystallize from molten rock, and from metamorphic rocks, which start as existing rocks that are altered by heat and pressure. Limestone is also sedimentary, but it’s made mainly of carbonate minerals derived from shells or chemical precipitation, not sand-sized grains, so it’s not sandstone.