Sedimentary Rocks

Sedimentary rocks form by the burial and cementation of loose sediments near the Earth's surface and are often characterized by their layered particles. Many of the sediments from which these rocks form were originally deposited by water, and fossils are nearly always found in sedimentary rocks. Sedimentary rocks may be clastic, meaning that they are composed of lots of individual pieces (often rounded) of earlier rocks that have been weathered, eroded and deposited in some sedimentary environment at/near the Earth's surface. Alternatively, sedimentary material may have formed as a chemical/biochemical precipitate directly from surface waters like the ocean or a large lake. In that case the rocks may be crystalline or may contain a very large fraction of shell material (biologically precipitated minerals).

CLASTIC SEDIMENTARY ROCKS
		CONGLOMERATE - consists of rounded large particles (greater than 2 mm in diameter on the average); might've formed from sediments deposited along a stream channel or some other high energy environment, where transport of such large particles would be possible
		SANDSTONE - consists of individual sand-sized particles (visible to the unaided eye, with an average diameter in the range 1/16-2 mm); might've formed from sediments deposited as a sand bar along a river, on a beach, or as dune sands in a desert. Some sandstones, like the one shown at left, are relatively poorly cemented and sand grains are easily dislodged. Other sandstones may be much better-cemented and much more durable.
		MUDSTONE - consists of individual particles too small to be seen by the unaided eye (less than 1/16 mm in diameter on the average); might've formed from muddy floodplain sediments or from offshore muds and often contains fossils. Colors of mudstones are highly variable, ranging from greenish and purplish to blacks, browns and reds.
CHEMICAL/BIOCHEMICAL SEDIMENTARY ROCKS
		LIMESTONE - typically forms from shallow-water (continental shelf) oceanic sediments in tropical regions. In such areas a significant fraction of the sediment consists of the shells of organisms (which are often microscopic) that have collected on the sea floor after the organisms died. Because the shells are made of calcite, this rock will fizz with a drop of dilute hydrochloric acid. Limestones often contain larger fossils as well.

Igneous Rocks

Metamorphic Rocks

Common Rocks

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