Post on 17-Jan-2016
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
Sandstone = formed where sand is laid and buried – beaches, dunes, and seafloors
Shale = forms from the compaction of silt and clay-size mineral particles
Monument Valley in Arizona
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
Clastic Sedimentary Rock
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 withnaturally occurringchalk, you’re crushingand smearing the calcite-shell remains of once-living ocean organisms.
already-existing already-existing rocks that are rocks that are weathered and weathered and
erodederoded
forms when sediments are forms when sediments are pressed and cemented pressed and cemented
together, or when together, or when minerals form from minerals form from
solutionssolutions
ClasticClastic ChemicalChemical OrganicOrganic
Broken Broken fragments of fragments of other rocksother rocks
weatheringweathering
erosionerosion
compactioncompaction
cementationcementation
Dissolved minerals come out Dissolved minerals come out of solutionof solution
limestone HaliteHalite
Made of the Made of the remains of once remains of once
living thingsliving things
chalkchalk coalcoal