Sedimentary rocks form from the compaction and cementation of sediments like sand, silt, and clay. They make up the majority of Earth's surface but only a small percentage of its crust. Sedimentary rocks are formed through lithification, where pressure forces minerals to cement sediments together. There are three main types - clastic rocks which contain fragments, crystalline rocks formed from mineral precipitation, and bioclastic rocks consisting of plant and animal remains.

1. SEDIMENTARY ROCKS
• Sedimentary rocks
form from various types
of sediment.
• Sedimentary rocks make up 90% of
SURFACE rocks and only about 1% of
Earth’s crust.

2. How are Sedimentary Rocks
Formed
• Sedimentary rock forms when sediments are
combined to form solid rock
• “Lithification” is the fancy name for forming rocks.
• Sedimentary rock is formed in two ways:
– Compaction
• Formed by pressure compacting the sediments
together
AND/OR
– Cementation
• Pressure forces water out of the sediments, the
dissolved mineral crystallize, cementing the
sediments together

3. “Overburden” is extra stuff on top. More
sediment, a continent, whatever.
Compaction and Cementation
of Clastic Sediment into Rock
Overburden

4. Three Kinds of Sedimentary Rocks
• 1. Clastic – fragments of other rocks. For
example: shale, sandstone, conglomerate
• 2. Crystalline – formed from mineral grains that
fall out of solution by chemical action or
evaporation. For example: Rock salt and
chemical limestone.
• 3. Bioclastic – formed from remains of plants
or animals. For example: Coal and limestone
from shells (coquina).

5. How are Clastic Sedimentary
Rocks formed
• Sediment is deposited and then
goes through the process of
lithification (forming sediment into
sedimentary rocks)

6. How are Clastic Sedimentary
Rocks formed
Weathering
Erosion
Deposition
Lithification

7. Clastic Sedimentary Rocks
• Clastic sedimentary rocks are characterized
based on their grain size.

8. How are Clastic Sedimentary
Rocks formed.
• Grain sizes vary from Coarse (pebbles,
cobbles, boulders) to Medium (sand) to
Fine (silt and clay).

9. Grain Sizes
Boulders
Cobbles
Coarse Gravel
Fine Gravel
Coarse / Medium Sand
Fine Sand – Powdered Sugar
Silt - Powder

10. Mixed

11. How Does The Sediment Get
Sorted Into Different Sizes?
• Running water (rivers, streams, creeks) pick up
sediment and carry it along its travels.
• The faster the water is moving, the larger the
particle that can be carried, and vice-versa.
• When a river hits a larger body of water, like a
lake or ocean, it’s like hitting a brick wall. This
results in the river “dumping it’s load” – dropping
all the sediment it’s been carrying.
• The sediment gets dumped according to size!

12. How Does The Sediment Get
Sorted Into Different Sizes?
• The bigger sediment gets deposited
FIRST, since it’s bigger, heavier and sinks
first.
• Then, the sediment gets gradually
SMALLER the farther you go from where
the river hits the lake or ocean.
• Therefore, coarse clastic rocks get made
where the larger sediment gets deposited
and the medium to fine clastic rocks get
made further away from that point.

14. Clastic Sedimentary Rocks
Conglomerate
– made of pebbles
and/or cobbles
cemented together
by sand, silt and
clay. Coarse-
grained
Sandstone –
sand that has
been cemented
together.
Medium-grained
Shale – made
from clay. Fine-
grained

16. Crystalline Sedimentary Rocks
• Also called chemical sedimentary rocks.
• Chemical action or evaporation causes
minerals to drop out of solution.
• This process creates chemical or crystalline
sedimentary rocks.
• For example: Calcite will precipitate out of
water and build-up to form chemical
limestone (it will fizz with acid since it has
calcite in it!)

17. Crystalline (Chemical) Sedimentary
Rocks
Gypsum Rock –
made when the mineral
gypsum precipitates out
of water.
Chemical
Limestone

18. What happens when salty water
evaporates and just salt is left
behind?
Bonneville Salt Flats of the Great Salt
Lake, Utah. The lake bed is covered
with rock salt which gives it the white
color. The salt is mined by the Morton
Salt Company.

20. Bioclastic (Organic) Sedimentary
Rocks
• Also called Organic sedimentary rocks.
• Formed from once-living things like plants
and animals.
• For example: Plants die and decay and
form coal.
• Another example: Shells can get broken
up and cemented back together to form
organic limestone (also called coquina).

21. Bioclastic (Organic) Sedimentary
Rocks
Coal
Organic Limestone
or Coquina

22. Bioclastic Rock

24. Answers
1. Define Clastic-
2. Define bioclastic-
3. What type of rock is made of particle .05 cm?
4. What type of rock is made of particle .1 cm?
5. What is the chemical composition of bituminous
coal?
Made from fragments of other rocks
Formed from remains of plants or animals
Sandstone
Sandstone
Carbon