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This image of Australia's Great Barrier Reef shows organic sedimentary rocks in production!
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Courtesy of Abi Howe, American Geological Institute

Organic Sedimentary Rocks

The sediment in an organic sedimentary rock is made of fossils!

The hard parts of animals, such as bones and shells, can become cemented together over time to make rock. Usually the bones and shells are made of calcite, or similar minerals, and the organic rock that is made from them is called limestone. Some types of microorganisms that live in the ocean or lakes have tiny skeletons made of silica. The organic rock made from their skeletons is called chert.

Plant remains squashed deep underground over millions of years make an organic sedimentary rock called coal. Coal doesn’t look like it is made of sediment. It is also often difficult to see the plant fossils within it because they have become so compacted over time, the less stable materials have left, and all that remains is carbon.

Last modified August 25, 2003 by Lisa Gardiner.

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TES XXVI, 3 fall 2010 The Fall 2010 issue of The Earth Scientist, focuses on rocks and minerals, including articles on minerals and mining, the use of minerals in society, and rare earth minerals, and includes 3 posters!

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