Lesson 2.4: Sedimentary Rocks
Sediment
Study Guide
small, solid pieces of material that come from rocks or living things (pebbles, mud, shells, leaves)
Key Idea: Most sedimentary rocks are formed through a sequence of processes: weathering, erosion, deposition,
compaction, and cementation.
Weathering
the breaking up of rock due to freezing and thawing, plant roots, acid, and other forces
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Erosion
the process by which running water, wind, or ice carry away bits of broken-up rock
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Deposition
the process by which sediment settles out of the water or wind carrying it
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Compaction
the process that presses sediments together
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Cementation
the process in which dissolved minerals crystallize and glue particles of sediment together
Key Idea: The three major groups of sedimentary rock are clastic rocks, organic rocks, and chemical rocks.
Clastic Rock- sedimentary rock formed when rock fragments are squeezed together
 Clastic rocks are grouped by the size of the rock fragments they contain.
Shale
 Forms from tiny particles of clay deposited in thin, flat layers
Sandstone
 Forms from sand on beaches, ocean floor, riverbeds, and sand dunes
 Most sand particles consist of quartz
Conglomerate
 Rock fragments with rounded edges
Breccia
 Rock fragments with sharp edges
Organic Rock- sedimentary rock formed where the remains of plants or animals are deposited in layers
Coal
 Forms from the remains of swamp plants buried in water
Limestone*
 Forms in the ocean where living things, such as coral, clams, and oysters, have
deposited hard shells and skeletons after they have died.
Chemical Rock- formed when minerals dissolved in a water solution crystallize, or from mineral deposits left when
seas or lakes evaporate.
Halite
 Rock salt forms by evaporation
Limestone*
 forms when calcite is dissolved in a solution, and then crystallizes
Key Idea: People have used sedimentary rocks throughout history for many different purposes, including for
tools and building materials.
Spearheads
Chert and Flint- hard, but can be shaped to a point
Building
Materials
Sandstone and Limestone- soft enough to be cut into bricks and slabs