sedimentary rocks

sediments

Most sedimentary rocks form from sediments. Sediments are small pieces of other rocks, like pebbles, sand, silt, and clay. Sedimentary rocks may include fossils. Fossils are materials left behind by once-living organisms. Fossils can be pieces of the organism, like bones. They can also be traces of the organism, like footprints. Most often, sediments settle out of water (Figure 4.13). For example, rivers carry lots of sediment. Where the water slows, it dumps these sediments along its banks, into lakes and the ocean. When sediments settle out of water, they form horizontal layers. A layer of sediment is deposited. Then the next layer is deposited on top of that layer. So each layer in a sedimentary rock is younger than the layer under it. It is older than the layer over it. Sediments are deposited in many different types of environments. Beaches and deserts collect large deposits of sand. Sediments also continuously wind up at the bottom of the ocean and in lakes, ponds, rivers, marshes, and swamps. Avalanches produce large piles of sediment. The environment where the sediments are deposited determines the type of sedimentary rock that can form.

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sedimentary rock formation

Sedimentary rocks form in two ways. Particles may be cemented together. Chemicals may precipitate.

clastic rocks

Over time, deposited sediments may harden into rock. First, the sediments are compacted. That is, they are squeezed together by the weight of sediments on top of them. Next, the sediments are cemented together. Minerals fill in the spaces between the loose sediment particles. These cementing minerals come from the water that moves through the sediments. These types of sedimentary rocks are called clastic rocks. Clastic rocks are rock fragments that are compacted and cemented together. Clastic sedimentary rocks are grouped by the size of the sediment they contain. Conglomerate and breccia are made of individual stones that have been cemented together. In conglomerate, the stones are rounded. In breccia, the stones are angular. Sandstone is made of sand-sized particles. Siltstone is made of smaller particles. Silt is smaller than sand but larger than clay. Shale has the smallest grain size. Shale is made mostly of clay-sized particles and hardened mud.

chemical sedimentary rocks

Chemical sedimentary rocks form when crystals precipitate out from a liquid. The mineral halite, also called rock salt, forms this way. You can make halite! Leave a shallow dish of salt water out in the Sun. As the water evaporates, salt crystals form in the dish. There are other chemical sedimentary rocks, like gypsum. Table 4.1 shows some common types of sedimentary rocks and the types of sediments that make them up. Picture Rock Name Conglomerate Type of Sedimentary Rock Clastic Breccia Clastic Sandstone Clastic Siltstone Clastic Limestone Bioclastic Coal Organic Picture Rock Name Rock Salt Type of Sedimentary Rock Chemical precipitate

instructional diagrams

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questions

Types of sediments that may make up sedimentary rocks include

a. pebbles.

b. silt.

c. clay.

-->  d. all of the above

What are solid particles that have been deposited on the Earths surface called?

a. lava

-->  b. sediments

c. quartz

d. soils

A river deposits sediments when the water

a. slows down.

b. enters a lake.

c. reaches the ocean.

-->  d. all of the above

Which of the following has the smallest grains?

a. breccia

b. conglomerate

-->  c. siltstone

d. sandstone

Which of the following sedimentary rocks contains the smallest sediments?

a. conglomerate

b. sandstone

c. siltstone

-->  d. shale

The processes by which sediments harden into rock include

-->  a. compaction

b. sedimentation

c. dissolution

d. precipitation

Clastic sedimentary rocks are classified by

a. the presence or absence of fossils

b. how hard they are

-->  c. the size of the sediments they are made of

d. the location where they precipitated

Which of the following rocks is not a clastic sedimentary rock?

a. limestone

b. breccia

-->  c. halite

d. two of the above

The White House in Washington, D.C., is made of

a. clastic rock.

b. sedimentary rock.

c. sandstone.

-->  d. all of the above

Which of the following is NOT a fossil?

a. dinosaur footprints

b. mammoth bones

c. ancient human hair preserved in cave sediments

-->  d. a modern shell on the beach

When sediments settle out of water, they form

a. chemical rocks.

-->  b. horizontal layers.

c. precipitates.

d. none of the above

Which sedimentary rock is formed of rounded stones that have been cemented together?

a. breccia

b. sandstone

-->  c. conglomerate

d. limestone

Sandstone is very porous so water can move easily through it.

-->  a. true

b. false

Sedimentary rocks may contain fossils.

-->  a. true

b. false

Avalanches produce horizontal layers of sediments.

a. true

-->  b. false

Like minerals, rocks cannot include organic materials.

a. true

-->  b. false

Particles of silt are smaller than particles of clay.

a. true

-->  b. false

Breccia and conglomerate have large sediments that have different shapes.

-->  a. true

b. false

Fossils are always the remains of bones or teeth.

a. true

-->  b. false

Sediments are pieces of rock.

-->  a. true

b. false

Coal is not a sedimentary rock.

a. true

-->  b. false

Sediments on a beach may include cobbles and pebbles.

-->  a. true

b. false

Cementation occurs when the fluids in the free spaces of the sediments crystallize.

-->  a. true

b. false

A rock that includes fossil fragments is a bioclastic rock.

-->  a. true

b. false

All sedimentary rocks form from sediments.

a. true

-->  b. false

Shale may contain hardened mud.

-->  a. true

b. false

Limestone is a chemical sedimentary rock.

a. true

-->  b. false

type of sedimentary rock that forms when crystals precipitate out of liquid

a. cemented

b. clastic sedimentary rock

c. compacted

d. sandstone

e. rock salt

f. fossil

-->  g. chemical sedimentary rock

squeezed together by upper layers of sediments

a. cemented

b. clastic sedimentary rock

-->  c. compacted

d. sandstone

e. rock salt

f. fossil

g. chemical sedimentary rock

type of sedimentary rock that forms when rock fragments are compacted and cemented together

a. cemented

-->  b. clastic sedimentary rock

c. compacted

d. sandstone

e. rock salt

f. fossil

g. chemical sedimentary rock

preserved material left behind by a once-living organism

a. cemented

b. clastic sedimentary rock

c. compacted

d. sandstone

e. rock salt

-->  f. fossil

g. chemical sedimentary rock

stuck together by minerals that fill in spaces between sediments

-->  a. cemented

b. clastic sedimentary rock

c. compacted

d. sandstone

e. rock salt

f. fossil

g. chemical sedimentary rock

example of a clastic sedimentary rock

a. cemented

b. clastic sedimentary rock

c. compacted

-->  d. sandstone

e. rock salt

f. fossil

g. chemical sedimentary rock

example of a chemical sedimentary rock

a. cemented

b. clastic sedimentary rock

c. compacted

d. sandstone

-->  e. rock salt

f. fossil

g. chemical sedimentary rock

diagram questions

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