2.4 Sedimentary Rocks

sedimentary rock – small particles of rocks or the remains of plants and animals are pressed and cemented together, forming flat layers sediment – small, solid pieces of materials that come from rocks or living things. Fossils are usually found in sedimentary rocks

Most sedimentary rocks are formed through a sequence of processes (5 steps): weathering erosion deposition compaction cementation

weathering (to weather, weathered, weathers, etc.) – to break rock ice, water, and wind usually weather (break) the rock erosion (to erode, eroding, erodes) – to carry / move rock ice, water, and wind usually erode (carry away) the rock

deposition (to deposit, depositing, deposits) – to drop rock ice, water, and wind usually deposit (drop) the rock if the rock is deposited into a lake or ocean, the rock will sink to the bottom forming layers compaction (to compact, compacting, compacts) – to squeeze rock sediments together sediment building up gradually over millions of years can cause compaction the weight of new layers can squeeze older sediments together

cementation (to cement, cementing, cements) – to glue rock sediments together some minerals in the rock slowly dissolve in the water these dissolved minerals crystallize and glue particles of sediment together

The three major groups of sedimentary rocks are: clastic rocks organic rocks chemical rocks

clastic rock – a sedimentary rock that forms from particles of other rocks. The grains (fragments) can vary in size from fine to coarse. Clastic rocks are group by the size of their rock fragments (grains) of which they are made.

4 types of clastic sedimentary rocks: shale forms from tiny particles of clay – water deposits the clay particles in thin, flat layers sandstone form from sand – most sand particles have a mineral called quartz in them conglomerate is made up of many rounded particles breccia is made up of many jagged sharp particles

2 types of organic rocks are: organic rocks – sedimentary rocks that form from dead plants and animals that were deposited in layers 2 types of organic rocks are: Coal forms from the remains of swamp plants buried in water. Many layers of plant remains build up, the weight of the layers squeezes the dead plants together, and over millions of years, they slowly change into coal Limestone forms in the ocean, where many ocean animals have hard shells or skeletons. When these ocean animals die, their shells pile up on the ocean floor. Compaction & cementation change them into limestone.

chemical rocks – forms when minerals dissolved in a water solution crystallize For example: limestone chemical rocks can also form when mineral deposits are left in a sea or lake that has evaporated For example: rock salt

Like igneous rocks, sedimentary rocks are also used for tools and building materials.

Pull out sandstone, breccia, shale, conglomerate, and limestone? How are they the same? How are they different? They are all sedimentary rocks. Sandstone, shale, and limestone are all fine-grained. Breccia and conglomerate are all coarse-grained. Sandstone, breccia, shale, and conglomerate are all clastic. Limestone is both organic and chemical.