SEDIMENTARY ROCKS

Classification of Rocks

Classification of Rocks

Rocks are aggregates of minerals. Geologists divide rocks into three groups: igneous, metamorphic, and sedimentary.

Igneous rocks crystallize from magma. Metamorphic rocks form by the deformation and/or

recrystallization of pre-existing rock by changes in temperature, pressure, and/or chemistry.

Sedimentary rocks form by weathering and erosion of preexisting rock to make sediment, which is lithified into rock.

ROCK CYCLE

SEDIMENTARY ROCKS IN THE ROCK CYCLE

Sedimentary rocks form from pre-existing rock particles - igneous, metamorphic or sedimentary. The Parent rock undergoes WEATHERING by chemical and/or physical mechanisms into smaller particles. These particles are TRANSPORTED by ice, air or water to a region of lower energy called a sedimentary basin. DEPOSITION takes place as a result of a lowering of hydraulic energy, organic biochemical activity or chemical changes (e.g., solubility).

Once deposited, the sediments are LITHIFIED (turned into rock) through COMPACTION (decrease in rock volume due to weight of overlying sediment) and CEMENTATION (chemical precipitation in pore spaces between grains which "glues" the rock together. The primary mineralogical and textural characteristics of the rock can be modified as the sediments are buried deeper in the earth's crust and undergo an increase in both temperature and pressure.

KINDS OF SEDIMENTARY ROCKS

Sedimentary rocks: Rocks that are produced by the action of weathering and erosion that break down pre-existing rocks by physical and chemical processes. Sediment is the stuff that is transported by wind, water or ice to a site of deposition. There are three types of sediments:

clastic sediments: made of particles of various sizeds carried in suspension by wind, water or ice. sand is an example of a clastic rock.

chemical sediments: precipitated from water. Halite (salt) is an example of a chemical rock.

organic sediments: precipitated or accumulated by biological means. Many plants and animals precipate hard parts made for example of calcite and leave organic sediments behind. Limestone is an example of an organic sediment.

SEDIMENTARY PROCESSES

Clastic Sedimentary Rocks: Conglomerate

Conglomerate rocks come from gravel “glued” together by lime.

Look at the difference in gravel in these two. What does it tell you about the conditions under which the rocks formed?

Clastic Sedimentary Rocks:Sandstone Sandstone is made up

of smaller particles, like sand, that are glued together by lime.

What do the lines represent or tell you?

Can sand be either sharp or smooth?

Clastic Sedimentary Rocks:Shale

Shale is made from even finer particles than sand, like clay, but still glued together with lime.

Shale is usually dark, with lots of organic remnants and fossils, and is always layered.

Kinds of Limestone

Chalk cliffsof Dover Englandare limestone fromtiny diatoms, singlecelled water creatures

Coral Reefs are a kind of limestone,based on animals that live in warm salt water.

This is massive limestone, apeak known as El Capitan in Texas. Limestone is always the mineral calcite, calciumcarbonate, usually producedby marine animals.

Evaporite Minerals

This is a salt flat in Death Valley California. Gypsum, halite, and borax are evaporite minerals that are formed from salt water evaporating.

COAL

COAL

Coal Mine Coal Fields in the USA