Sedimentary Rocks Sedimentary rocks form when sediments harden into rocks 3 main kinds clastic, chemical and organic Most of Earth’s crust is covered by sedimentary rocks

Three Main Kinds of Sedimentary Rock  Clastic:cemented together fragments of other rocks  Chemical:mineral grains that are removed from a solution by evaporation or chemical action  Organic: remains of plants and animals

Clastic Rocks  Clastic sedimentary rocks are made up of weathered rocks that already exist  Rocks are weathered and transported by rivers, winds, waves, and glaciers  Sediments are deposited when the transport system loses energy ie: stream  Ocean water, lake water, and groundwater contain natural cements: silica(SiO 2 ), calcite (CaCO 3 ), and iron oxide(FeO)  These dissolved minerals settle into the spaces between the sand grains or pebbles, binding them together into rock  The pressure of overlying sediments can also make fine sediments stick together

Clastic Rocks: Conglomerate Coarse, large grains Deposited in high energy system (rough water) Cemented mixture of rounded pebbles and sand grains Pebbles can be any durable rock material

Clastic rocks: Sandstone Medium grained Quartz grains (7 on Moh’s scale of hardness) Porous (small holes) Permeable (water can pass through)

Clastic rocks: Shale  Fine grained clay minerals  Impermeable  Smooth, soft and easily broken  Found in very low energy environments

Sorting of Sediments

Chemical Sedimentary Rocks  Dissolved minerals fall out of solution  Evaporation or the combining of dissolved ions to form new minerals.  The most common are limestone, rock salt, and rock gypsum  Limestones are formed from tiny grains of calcite  Rock salt is the natural form of table salt, it is almost pure halite  Rock gypsum occurs in layers and is almost pure gypsum

Chemical Sedimentary Rocks Rock Salt Limestone

Organic Sedimentary Rocks  Organic sediments come from the remains of plants and animals  The most common are shell limestone and coal  shell limestone is mostly calcite, shell producing animals die and their shells pile up and are cemented together

Sedimentary Features: Stratification  Stratification is the arrangement of rocks in visible layers  When there is a change in the type of sediments being laid down, new rock layers are formed  Change results from new source sediments or energy change  The layers are called beds and are separated by bedding planes

Sedimentary Features: Cross Bedding  Cross-bedding develops when beds are deposited at an angle: wind on dunes, rivers on deltas or sandbars

Fossils in Sedimentary Rocks  Animals and plants that die and are buried, as sediments pile up= fossils  The hard parts may remain as fossils when the sediments turn to rock  Fossils are the remains, impressions, or any other evidence of plants and animals preserved in rock

Ripple Marks and Mud Cracks  Many sandstones show ripple marks that are formed by the action of winds, streams, waves or currents on sand.  Mud cracks develop when deposits of wet clay dry and contract  Mud cracks are later filled with different materials, and the clay becomes shale rock.

Nodules, Concretions, Geodes  Nodules are lumps of fine-grained silica called chert, solid replacement bodies  Concretions are round masses of mineral precipitation that form around some kind of nucleus  A Geode is a hollow nodule of silica rock, filled with crystals of quartz or calcite Nodule Geode