For example, little waves or ripple marks may develop in the sand on a beach. The rock that forms from that sand may have rippled lines. Another common feature is mud cracks, which develop when the sediment at a bottom of a river or stream goes through cycles of flooding and drying. A special type of concretion is a geode, whose hollow interior is lined with crystals. A Sequoia stem and alder leaf fossilized in sedimentary rock.
Sedimentary rocks are also the source of most fossils.
Because older rocks contain simpler fossils, the age of a rock can be estimated by looking at any fossils in it. The color of sedimentary rock is another clue to the chemical composition of the sediments from which it formed. The bands of red and pink rocks in the Grand Canyon, for example, come from iron-bearing minerals such as hematite. Sedimentary rocks cover almost all of the ocean floor and about three-fourths of Earth's surface land area. Like igneous rocks, sedimentary rocks may undergo changes that transform them into new, metamorphic rocks.