3. ROCKS defined
Are naturally occurring solid mixtures of one or more minerals.
Rocks are classified by how they are formed, their composition, and texture
Rocks change over time through the rock cycle
4. TYPES OF ROCKS
Rocks are divided into three groups based on
how rocks are formed:
5. IGNEOUS ROCKS
• Igneous rocks are formed by the cooling
and hardening of molten rocks
6. TYPES OF IGNEOUS ROCKS
EXTRUSIVE / VOLCANIC ROCKS
• Forms at the surface.
• When magma reaches the surface it is called
Lava. Lava cools and hardens to form
•When the cooling is very fast (almost instant)
it will form rocks without crystals (glassy
texture) e.g. Obsidian, while if it is not that fast
it will form tiny crystals (fine-grained) e.g.
13. INTRUSIVE / PLUTONIC ROCKS
Magma does not always reach the surface but may solidify
below the Earth’s surface. In this case it forms Intrusive
Since the magma takes a longer time to solidify below the
surface, the rocks formed have bigger crystals e.g. Granite
21. SEDIMENTARY ROCKS
Sedimentary rocks are
formed by erosion.
Sediments are transported
and deposited in layers,
with the older ones on
The layers become
compacted and cemented
together to form rocks.
22. They are also formed as a result of exogenic
processes e.g. chemical & mechanical weathering,
freezing & thawing, oxidation.
Sedimentary rocks usually occur in layers (Strata)
Stratification is the process
by which sedimentary rocks
are arranged in layers.
2) Chemical sedimentary rocks such as rock salt and
some limestones, form when dissolved materials
precipitate from solution. Minerals crystallize out of
solution to become rocks e.g. limestone.
30. 3) Organic sedimentary rocks
such as coal and some limestones which
form from the accumulation of plant or
34. METAMORPHIC ROCKS
means to change
Metamorphic rocks can
also be modified by
chemical process while
buried deep below Earth's
surface. Exposure to
these extreme conditions
will alter the mineralogy,
texture and chemical
composition of the rocks.
35. Metamorphic rocks can be Foliated,
i.e. showing layers / bands of
minerals e.g. Gneiss or Non- Foliated e.g. Marble
40. USES OF ROCKS
1. Source of minerals e.g. gold
2. Used in construction
3. As aquifers, they are good sources of water
4. They form mountains, which are places of
scenic beauty e.g. Mulanje mountain, Africa
41. THE ROCK CYCLE
from one form
any type of rock
can change into
into sedimentary or metamorphic and vice versa.
42. ROCK QUIZ
1. What geologic process changes pieces of rocks,
minerals and other material into sedimentary rock?
a) Compacting and cementing
c) Heat and Pressure
43. 2. What element is missing from this diagram of the
a) Sedimentary rock
b) Compacting and cementing
d) Metamorphic Rock
45. 4. What geologic process can change granite
(igneous rock) into gneiss (metamorphic rock)?
a) Compacting and cementing
c) Heat and Pressure
46. 5. The process that shows how one rock can
change into another is called
a) The metamorphic cycle
b) The mineral cycle
c) The clastic cycle
d) The rock cycle
47. 6.Mount Rushmore National Memorial located in South
Dakota is a monumental granite sculpture of the 3
presidents George Washington, Thomas Jefferson,
and Theodore Roosevelt. What rock type is granite?
d) None of the above.
48. 7. Geologists divide rocks into three
groups: metamorphic, sedimentary, and
49. 8. When magma cools quickly, what kind of texture
or crystals does a rock have?
a) coarse-grained or large crystals
b) a mixture of all types of grains or sizes of crystals
c) medium-grained or medium crystals
d) fine-grained or small crystals
50. 9.The seated sculpture of President Lincoln inside
the Lincoln Memorial was carved out of white
Georgia marble. What type of rock is marble?
d) None of the above
Breccia is a clastic sedimentary rock that is composed of large (over two millimeter diameter) angular fragments. The spaces between the large fragments can be filled with a matrix of smaller particles or a mineral cement which binds the rock together.
Sandstone is a clastic sedimentary rock made up mainly of sand-size (1/16 to 2 millimeter diameter) weathering debris. Environments where large amounts of sand can accumulate include beaches, deserts, flood plains and deltas.
Shale is a clastic sedimentary rock that is made up of clay-size (less then 1/256 millimeter in diameter) weathering debris. It typically breaks into thin flat pieces.
Limestone is a rock that is composed primarily of calcium carbonate. It can form organically from the accumulation of shell, coral, algal and fecal debris. It can also form chemically from the precipitation of calcium carbonate from lake or ocean water. Limestone is used in many ways. Some of the most common are: production of cement, crushed stone and acid neutralization.
Rock Salt is a chemical sedimentary rock that forms from the evaporation of ocean or saline lake waters. It is also known by the mineral name "halite". It is rarely found at Earth's surface, except in areas of very arid climate. It is often mined for use in the chemical industry or for use as a winter highway treatment. Some halite is processed for use as a seasoning for food.
Foliated Metamorphic Rocks have a layered or banded appearance that is produced by exposure to heat and directed pressure. Non-foliated metamorphic rocks such as marble and quartzite which do not have a layered or banded appearance.
Schist is metamorphic rock with well developed foliation. It often contains significant amounts of mica which allow the rock to split into thin pieces.
Phyllite is a foliate metamorphic rock that is made up mainly of very fine-grained mica. The surface of phyllite is typically lustrous and sometimes wrinkled. It is intermediate in grade between slate and schist.
Quartzite is a non-foliated metamorphic rock that is produced by the metamorphism of sandstone. It is composed primarily of quartz.