sedimentary rocks sedimentary rocks form when sediments harden into rocks 3 main kinds clastic,...
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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(SiO2), calcite (CaCO3), 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
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