http://z.about.com/d/geology/1/0/R/N/sandstone.jpg
Sedimentary rocks
Sedimentary rocks consist of material that has been
deposited one layer at a time, either in water
(examples: beach, lakeshores) or in air
(example: sand dunes).
Sedimentary rocks often have obvious layering
and individually distinct grains.
Sandstone is the most obvious example
(and we're surrounded by it here in
Northern Arizona).
http://z.about.com/d/geology/1/0/R/N/sandstone.jpg
The other famous sedimentary rock is
limestone, which is made of crushed and
compacted and cemented seashells.
http://www.beg.utexas.edu/mainweb/publications/graphics/limestone.htm
Limestone often has seashells (or fossils) in it.
Limestone also fizzes when you drip hydrochloric
acid (HCl) on it.
Limestone can have less obvious grains and stratigraphy
than sandstone.