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."

Definition: a rock that forms from layers of sand-sized pieces of quartz
Type: sedimentary
Appearance: sandy; may be layered; colors include tan, brown, red
Grain size: medium (about the size of sand)
Primary mineral: quartz
Cool fact: Sandstone is found in some of the world's most spectacular formations, like the Grand Canyon.

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