Review

What determines the size of the mineral grain in an igneous
rock?

Explain when magma will form a coarse-grained rock, a
fine-grained rock, or glassy rock?

What factors favor the growth of large crystals?

What are extrusive rocks? Why are they easy to recognize as
igneous?

What are intrusive rocks? Hoe do geologists know they are
igneous?
Sedimentary Rock
Sedimentary Rocks: (definition)
• Formed by hardening and cementing of layers of sediments
(rock fragments, organic remains, or chemicals that form on lake
or ocean bottoms)
• 75% of Earth’s surface covered with sediments & sedimentary
rocks
Sedimentary Rock
3 types:
A) Clastic Sedimentary Rocks
B) Chemical Sedimentary Rocks
C) Organic Sedimentary Rocks
A) Clastic

Formed from fragments of other rocks.
Formation:

i) pre-existing rocks are weathered

ii) the fragments are transported by wind, ice, and water
(*the further the fragments travel, the more rounded they
become)

iii) the fragments are deposited according to energy and size
= sorting
 Large fragments = high energy = rivers
 Medium fragments = med energy = beaches
 Small fragments = low energy = lakes, oceans
A) Clastic
Examples:
• i) Shale – consists of tiny flakes of the mineral, little space.
• ii) Sandstone – made up of grains of quartz, with space between
particles.
• iii) Conglomerate – cemented mixture of rounded pebbles and sand
grains.
i
ii
iii
B) Chemical

Formed from minerals dissolved in sea, lake swamp or
underground.


Ex. Great Salt Lake, Dead Sea
Chemical sediments are formed when these minerals
are precipitated from the water by evaportaion.

Ex. Rock salt, Gypsum
B) Chemical
Great Salt Lake, Utah
C) Organic

Formed from remains of plants and animals

Limestone from the skeletons of shell fish

Coal from plants accumulating in shallow lakes or swamps

Chert from the skeletons of silica radiolarians and sponges
Sedimentary Features

Stratification

Fossils

Ripple Marks and Mud Cracks

Concretions and Geodes