Lets Rock!
THE ROCK CYCLE
ROCK
 is a naturally-occurring aggregate or
combination of minerals and mineraloids,
such as fossils and glass.
 Minerals are the building blocks of rocks,
rocks are the natural building blocks of
Earth’s lithosphere.
 Earth lithosphere is made primarily of rocks
containing one or more minerals.
The rock cycle involves processes
that destroy, generate, and
transform one rock from into
another.
3 Types of Rocks
There are 3
different
types of
rocks;
 Igneous
 Sedimentary
 Metamorphic
Igneous Rock
 Igneous rocks are formed by magma and lava
as it cools.
 The term ” Igneous ” is based from the Latin
ignis meaning fire.
 Igneous rocks are formed at high
temperatures.
 Magma or lava may be solidifies in one of the
three ways;
Below the surface- from
slow-cooling magma
 Rocks formed
have good
crystallization,
may become
plutonic rocks or
intrusive igneous
such as granite,
diorite, and
syenite
On the surface, from fastcooling lava
 Rocks formed
have no visible
crystals (fine
grained); may
become volcanic
rocks or extrusive
igneous, such as
basalt and
andesite.
On the surface, from the consolidation of
particles erupted by explosive volcanic
activity
 Rocks may become pyroclastic rocks like
ignimbrite, scoria, and pumice.
Igneous rock
Igneous rock
Sedimentary Rock
 Rocks accumulated on earth’s surface in a
process of deposition.
 Materials that make up sedimentary rocks are
combination of the products of weathering
and erosion, and organic materials
 The process by which these unconsolidated
materials become solidified into rock is called
lithification.
 Sedimentary rock is formed in layers.
Sedimentary Rocks
Limestone
Shale
Sandstone
Granite
Metamorphic Rock
 Metamorphic rocks are made from other
rocks (sedimentary or igneous rocks)
 High temperature and high pressure help
change an igneous or sedimentary rock
into a new kind of rock (think about how a
caterpillar becomes a butterfly)
CLASSIFICATION OF
ROCKS
Classification of rocks
 Classifying rocks is usually based on their
texture and composition
 Texture – refers to the size, shape, and
arrangement of mineral grains and other
constituents, which are controlled by
processes involved in the formation of the
rock.
Classification of rocks
 Rocks can also have distinct grain sizes:
aphanitic and phaneritic.
 Aphanitic – rocks have grains that are
too small to see or identify.
 Phaneritic – rocks have grains, which are
big enough to see.
Classification of rocks
 In igneous rocks, if the grain size is larger
than 1/16 mm, the rock is phaneritic. If the
grain is less than 1/16 mm, the rock is
aphanitic.
 In sedimentary rocks, the difference
between aphanitic and phaneritic is set at
1/1256mm.
 In metamorphic rocks, the difference
between aphanitic and phaneritic is less
quantifiable.
PARTS OF ROCKS
Rocks have many different parts
 Rocks can be sorted into groups
by looking at their parts. Some
rock parts are:
 Crystals
 Grains
Crystals
 Crystals are different atoms that are formed
in a pattern. They can be big or small, fat or
thin.
Grains
 Grains are smaller pieces of rock or sediment.
Grain size is something that is used a lot to
help decide the rock type.
Rock Explorers
 Lets look at some rocks!
 Get a partner and a magnifying glass
 Come and pick up a rock (you will be looking
at one rock at a time)
 You and your partner will take turns looking
at the rock. Decide if you think that crystals
are large or small. Look to see if it has grains.
ROCK-FORMING MINERALS
ROCK-FORMING MINERALS
 Minerals are composed of elements such as those
found in the periodic table. Each mineral is unique
but they generally exhibit the following
characteristics.
 They are naturally-occurring chemical compounds.
 They are inorganic.
 They are homogeneous solid.
 Although not fixed, each mineral has a definite
chemical composition which can be described by a
chemical formula.
 Each mineral’s structure arranges atoms in a
crystalline pattern.
ROCK-FORMING MINERALS
 Some minerals are made up of only
one element.
 Examples:
 Gold (Au)
 Graphite (C)
 Diamond (C)
 Copper (Cu)
ROCK-FORMING MINERALS
 The elemental composition of a mineral is
due to its unique optical and physical
properties such as:
- Luster
- Color
- Streak
- Hardness
- Cleavage
- Specific gravity
LUSTER
 Refers to the quality of light on the
surface of rock, crystal, or mineral.
 Minerals w/ high luster is very reflective.
Range of terms used to describe a
mineral’s luster – greasy, silky, metallic,
earthy, and vitreous(glass like).
COLOR
 The mineral’s color is caused by the
absorption, or lack thereof, of visible light by
their crystalline structure.
 Most minerals have color in various hues,
hence cannot be distinguished by color alone.
 Quartz, for example, maybe clear, white,
gray, brown, yellow, pink, red, or orange.
 color can help but do not rely on color as the
determining property
STREAK
 Streak is the color of a mineral’s powder.
Streak is a more reliable property than color
because streak does not vary.
HARDNESS
 Hardness is the strength with which a mineral
resists its surface being scraped or punctured.
 In working with hand samples without
specialized tools, mineral hardness is
specified by the Mohs hardness scale.
CLEAVAGE
 The tendency of a mineral to split or
cleave along planes of weakness.
SPECIFIC GRAVITY
 Measure of relative density of a mineral.
 It is determined by comparing its relative
mass to water.
 Specific gravity is not expressed in units of
any kind, as it is a ration
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑚𝑖𝑛𝑒𝑟𝑎𝑙
Specific gravity =
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑒𝑞𝑢𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟
SPECIFIC GRAVITY