Sedimentary Rocks

Formation of Sedimentary Rocks Sedimentary rock forms at or near the surface, when sediments are pressed and cemented together, or when minerals form from solutions. Sedimentary rocks often form as layers, strata. The process by which sediment becomes sedimentary rock is known as lithification.

What is sediment? Sediments are loose materials such as rock fragments, mineral grains, and remains of some organisms caused from Sediments come from weathered and eroded igneous, metamorphic, and sedimentary rocks.

Classifying Sedimentary Rocks Sedimentary rocks are classified by their composition and by the manner in which they formed. The three types of sedimentary rocks are: Clastic Chemical Organic

Clastic Sedimentary Rocks Clastic sedimentary rocks are made from the broken fragments of other rocks cemented together by a mineral. Clastic sedimentary rocks can have coarse-grained, medium-grained, or fine-grained textures Ex. Sandstone, breccia, conglomerate, shale

Shale = forms from the compaction of silt and clay-size mineral particles Sandstone = formed where sand is laid and buried – beaches, dunes, and seafloors

Monument Valley in Arizona

Clastic Sedimentary Rock Processes that help form sedimentary rocks: Weathering = Breaking down of material by wind, water, ice, sunlight, & gravity Erosion = Movement of sediments Deposition = The process by which sediment is dropped or settles in new locations. Compacted = Smaller sediments pushed together Cemented = Dissolved minerals such as quartz or calcite act as a natural glue cementing larger sediments together

Chemical Sedimentary Rocks Chemical sedimentary rocks form from solutions of dissolved minerals and water. Minerals crystallizes out of solution Ex. Halite, limestone, gypsum

Organic Sedimentary Rock Rocks made of the remains of once-living things are called organic sedimentary rocks. One of the most common organic sedimentary rocks is fossil-rich limestone. Coal- forms underground from plant material buried under sediment & changed to coal over millions of years

Example of Organic Sedimentary Rock Chalk is another organic sedimentary rock that is made of microscopic shells. When you write with naturally occurring chalk, you’re crushing and smearing the calcite-shell remains of once-living ocean organisms.

Organic Clastic Chemical coal erosion chalk weathering compaction forms when sediments are pressed and cemented together, or when minerals form from solutions already-existing rocks that are weathered and eroded Organic Clastic Chemical compaction Broken fragments of other rocks Made of the remains of once living things Dissolved minerals come out of solution cementation chalk coal Halite limestone weathering erosion