Sandstone is made of tiny pieces of sand you can see and feel. You can actually scratch away grains of sand from a piece of sandstone. It forms when wind, ice, and water carry away grains of sand and drop them someplace new—usually at the bottom and along sides of rivers, lakes, and coastlines. As more and more layers of sand build up, they become compacted to form a solid rock, held together by a natural "cement."

Image credits: main image, courtesy of AMNH; Rondi Davies: courtesy of AMNH.