Name ______________________________________________
Block ______
Sedimentary Rocks - Clastic Rocks
All sedimentary rocks come from sediments. Some sedimentary rocks are called clastic
because they are made of rock fragments. These fragments can be as small as microscopic clay
particles or as large as boulders. The type of rock that forms is the result of the sorting of
sediments that occurs when sediments are eroded and deposited elsewhere.
A river moves sediments into a lake. Particles are sorted by size. The largest gravels are
first to be deposited, followed by sands, and then silts and clays. Over time, the sediments are
buried and compacted. The particles may become cemented together.
Conglomerates form from the larger particles, sandstones from sands, and shale from silt and
clay. When minerals fill the spaces between sand and grains, they bind the fragments
together in a process called cementation.
When carried by a stream or river, the fragments become smooth and rounded from
rubbing against one another and the stream bed. The farther the particles are carried, the
more rounded they become.
Sedimentary Rocks - Chemical Rocks
The water in seas, lakes, swamps, and underground reservoirs often contains dissolved
minerals. Chemical sediments form when these minerals precipitate, or fall out of solution.
Precipitation can occur through evaporation or through chemical action. Common chemical
sedimentary rocks are rock salt, rock gypsum and some limestones. Rock salt, or halite, occurs
in thick layers in many parts of the world.
A thin layer of pooled, mineral-laden water bathes and slowly sculpts a portion of the Bonneville Salt Flats, east
of the twin desert towns of Wendover, Utah, and West Wendover, Nevada. The sheen slightly reflects the vault of the
blue sky, as shown in the photograph above, taken on April 23, 2013.
Winter and springtime snow and rainfall replenish and revive the surface minerals, including sodium chloride (table
salt), potassium and magnesium that compose the Bonneville Salt Flats; a 159 sq mi (412 sq km) pan left behind by the
prehistoric waters of vanished Lake Bonneville. The ancient lake covered much of western Utah and eastern Nevada
during the Pleistocene ice ages. Due to climate change and geologic factors, the great lake dried up thousands of years
ago, leaving behind only encrusted basins like this and a notable remnant, the Great Salt Lake.
Sedimentary Rocks - Organic Rocks
An organic sedimentary rock forms from sediments consisting of the remains of plants
and animals. Common organic sedimentary rocks are limestone and coal. Limestone organic
sedimentary rocks are formed from seashell sediments.
Coquina ("co-KEEN-a") is a limestone composed chiefly of shell fragments.
Limestone is a rock composed primarily of calcium carbonate. It can form organically from the accumulation of
shell and coral fragments. It can also form chemically from the precipitation of calcium carbonate from lake or
ocean water.
The single most characteristic feature of sedimentary rocks is stratification, the
arrangement of visible layers. A change in the type of sediment being laid down in one place
results in the formation of a new rock layer. For example, when sand is deposited on top of
clay, a layer of sandstone may form on top of a layer of shale. In this way, sedimentary rocks
become stratified. This can be caused by a river that brings sediment to an ocean or lake that
may break off and pick up new types of rock.
Sequences of sedimentary rock in the
Grand Canyon show the characteristic stratification or layering of this rock type (A). The cross section in (B) emphasizes
the layering and shows the difference between the sedimentary rocks and the older igneous and deformed metamorphic
rocks near the floor of the canyon.
Fill in the chart using the rock samples and your book. If there is more than one blank, then
you are looking for more than one sample. You should consider the following samples:
31, 32, 33, 37, 39, 40, 41, 42, 45, 48, 50, 51, 52, 54, 55, 56, 59, 63, 64, 68, 69
Sedimentary Rocks
Clastic
Chemical
Organic
Conglomerates - Sand and
round gravel cemented
together, sediment size varied
a.____________
b.____________
c.____________
Rock salt – rock form of halite,
reddish to tan in color (formed
from evaporation)
a.___________
Coal – black, made from
fossilized plant material
a.__________
Sandstones – Sand-sized grains
compacted and cemented
together
a.____________
b.____________
c.____________
Rock gypsum – rock form of
gypsum, pink to tan on color,
powered sugar appearance
(formed from precipitation)
a.____________
Fossil limestone – pieces of
shells cemented together
a.___________
b.___________
c.___________
Shales and claystone– clay-sized
grains invisible to the naked eye
a._____________
b._____________
c._____________
d._____________
Dolomite – pink to tan color,
crystal visible on surface
(formed from evaporation)
a. ________
Chalk – white, used to write on
slate
a.____________
Breccia – light-color, sand and
irregular pebble fragments
a.____________
Chemical limestone – light in
color, very dense
a. ________
Coquina – pieces of shells
compacted together (very little
other material)
a. ___________