Rock Classification Study Guide
Rocks are classified
into three major groups
Igneous, Sedimentary, and Metamorphic
Igneous
Formed by the cooling of the magma or lava
Sedimentary
Particles of other rocks or the remains of
Plants and animals pressed together
Metamorphic
Geologists classify and
Observe rocks by
Existing rock is changed by heat, pressure,
Or chemical reactions deep underground
Color, texture, mineral composition, and
Origin
What is texture?
The look and feel of a rock’s surface
Mineral composition?
Geologists will examine the crystal shape
And size, note reactions to acid and determine if the
mineral is magnetic
When studying rocks, geologists observe:
Color, Texture and Grains
Grain can be described by its size, shape, pattern or no visible grain
Grain size
Coarse
(large) grains that can be easily seen with
Or without a hand lens
Fine
(small) grains that can be seen only with
A microscope
Grain pattern
vary greatly
No Visible Grain
Crystals cooled so quickly that no crystals
Formed. Can have a glassy appearance made up of
small particles called silica
What is grain?
A particle of mineral or other rock that
Gives a rock its texture
Origin
Igneous rocks formed from magma and lava
IGNEOUS PRODUCTS
What is magma?
Magma is the molten mixture of rockForming substances, gases and water from the
Mantle.
What is lava?
Lava is liquid magma that reaches the surface.
Also the rock formed when liquid lava hardens.
Extrusive Rocks (volcanic)
Igneous rocks formed from lava that erupted out and
onto Earth’s surface (examples: basalt)
Intrusive (plutonic)
Igneous rocks formed when magma
Hardened in the Earth’s surface (beneath)
(Examples include granite)
Porphyritic texture –
large crystals scattered on a background of much
smaller crystals caused when a rock cools in two
separate stages
Lava low in silica
usually forms dark-colored rocks like basalt
Magma high in silica
usually forms light-colored rocks like granite
Why do different types of
Igneous rocks have different
Size grains?
It depends on how quickly lava cooled
What are some examples of
Igneous Rocks?
Granit, Basalt, Pumice,
Pegmatitie, Porphyry and Rhyolite
Uses
Some uses of igneous rocks include:
Granite
building materials
Basalt
road construction
Pumice
cleaning and polishing
SEDIMENTARY
What is sediment
Small solid pieces of material that
Come from rocks or living things
How do sedimentary rocks form
weathering, erosion, deposition,
Compaction and cementation
What does weathering mean
Wind and rain beat on rocks wearing
them down
What is erosion
occurs when the running water or
Wind loosen and carry away the
Fragments of rock
What is deposition
process when sediment settles
What is compaction
process that presses sediments
Together. The weight of the layers
Further compacts the sediments. The
Layers are often visible in sed. Rocks
What is cementation
The process in which dissolved
Minerals crystallize and glue particles
Of sediment together (can take millions
Of years for compaction and cementation
To transform loose sediments into rock
List the three major groups of
Sedimentary rocks
Clastic, Organic, and Chemical
What is Clastic
Forms when rock fragments are squeezed
Together
List Clastic Rocks
Shale, Sandstone, Conglomerate, and Breccia
What is Shale
Forms from tiny particles of clay. Water
Deposits the clay into very thin, flat layers
No cementation is needed to hold these
Together. Water cannot pass through and
Shale feels smooth and splits easily into
Flat pieces
What is Sandstone
Forms from sand. Most sand consists of
Quartz. Contains many small holes and water
Can absorb through these holes
What is Conglomerate
Contains fragments of different sizes
These rocks have rounded edges
What is Breccia
Contains fragments of different sizes
These rocks have sharp edges
List the Organic Rocks
Coal and Limestone
What is Coal
Coal forms from the remains of swamp
Plants buried in water. After years of
Compaction coal forms
What is Limestone
Consists of hard shells of living things.
After the shelled animals die, the shells
Pile up as sediment. After years and many
Layers, some shells dissolve forming a
Solution of calcite which bonds them
(chalk is a limestone)
What are the Chemical Rocks
Gypsum, Rock Salt and Limestone.
Chemical rocks form when minerals
dissolved in a solution are crystallized.
Limestone
is chemical and organic. When calcite that is
dissolved
In lakes come out of solution and forms
Crystals; this kind is chemical limestone
Rock Salt
Made from halite, which forms by evaporation
Gypsum
Formed by evaporation in dry climates
Uses of Sedimentary Rocks
Sandstone and limestone used for building
Materials
METAMORPHIC
How do metamorphic rocks form
Heat and pressure build up and change the
Rock
What are the two classifications
Foliated and Non Foliated
What is foliated
Grains are arranged in parallel layers
Examples: slate, schist and gneiss. These
Rocks can split apart on these layers
Slate
Heat and pressure turns shale into slate
What is non-foliated
The minerals are arranged randomly and
Not in layers. Examples: marble and
Quartzite
Marble
Heat and pressure turns limestone into marble
Quartzite
Heat and pressure turns sandstone into
Quarztite
Gneiss
Heat and pressure turns granite into gneiss
Parent rock
The rock before it changes into another rock
Uses of Metamorphic Rocks
Buildings (marble), floors, roofing,
Chalkboards (slate)
ROCK CYCLE
A series of processes on and beneath the earth’s surface that change rocks from one type of rock to
another type of rock.
( i.e. Magma to Igneous rock to Sedimentary rock to Metamorphic.)
Plate Tectonics
Plate movements drive the rock cycle by pushing rocks back into the mantle where they melt and
Become magma again.
Subducting Oceanic Plates
Under the ocean floor, plates move sandstone to the mantle, where it melts and forms
Magma, which eventually becomes igneous rock
Colliding Continental Plates
Collisions of continental plates can squeeze rocks from ocean floors and change sandstone
Into quartzite. They can also cause mountain ranges to form