Transcript Rocks

A rock is a naturally occurring solid mixture
composed of minerals, smaller rock
fragments, organic material, or glass. The
individual particles in a rock are known as
grains.
There three main types of rocks:
1. Igneous
2. Sedimentary
3. Metamorphic
Igneous rocks are the most abundant form of rock
on Earth. Igneous rocks are formed from magma or
lava. The type of magma will determine what type
of igneous rock will form. There four main types of
magma:
Felsic
2. Intermediate
3. Mafic
4. Ultramafic
1.
Felsic magma is thick and slow moving. It contains
large amounts of silica (SO2) and smaller amounts
of calcium, iron and magnesium. Igneous rocks
formed from felsic magma typically harden into
light colored silicate minerals such as quartz and
orthoclase feldspar.
Compared to felsic magma, mafic magma is much
hotter, thinner and faster moving. Mafic magma
contains large amounts of iron and magnesium and very
small amounts of silica. Rocks formed from mafic
magma are much darker in color due to large amounts
of dark silicate minerals such as biotite, augite, and
hornblend, olivine, and pyroxene.
There are two main types of igneous rock:
Intrusive
2. Extrusive
1.
Intrusive igneous rocks form below the Earth’s
surface and cool slowly. Characteristics of Intrusive
igneous rock include:
Course texture
2. Large grains
3. Large crystals.
4. Light-colored
1.
Extrusive igneous rock forms when lava cools and
crystallizes on the Earth’s surface. Characteristics of
extrusive igneous rock include:
Fine texture
2. Small grains
3. Small crystals.
4. Dark-colored
1.
Igneous rock is classified into three families:
1. Granite Family
2. Gabbro Family
3. Diorite Family
Rocks in the granite family form from slow-rising,
“sticky”, felsic magma that cooled slowly
underground. Granite can only be seen at the
surface as a result of uplift or weathering and
erosion.
Properties
Granite
Obsidian
Pumice
Color
Salmon, gray,
black
Smoky brown
Light gray
Luster
Dull with some
pearly and glassy
Glassy
Dull
7
5 -5.5
5 -5.6
Streak
No streak or white
White
White
Break
Fracture
Conchoidal
Fracture
2.6 – 2.7 g/cm3
2.6 g/cm3
.64 g/cm3
2.69
5
.64
Crystal Structure
Anhedral
None
None
Special Properties
-
Hardness
Density
Specific Gravity
Floats
Granite
Obsidian
Pumice
Igneous rock forms from mafic magma.
These rocks are dark in color, fine grained
and denser than rock in the granite family.
Properties
Scoria
Olivine
Basalt
Color
Reddish Brown
Greenish Black
Black, Dark gray
Luster
Glassy
Glassy
Dull
5-6
6.5 - 7
7
Streak
Reddish brown
White
Black
Break
Fracture
Conchoidal
Fracture
Density
2.6 g/cm3
3.32 g/cm3
3 g/cm3
Specific Gravity
.8 – 2.1
3.2 – 3.4
2.8 - 3
Crystal Structure
None
Orthorhombic
None
Special Properties
-
Hardness
Scoria
Gabbro
Olivine
Pyroxene
Basalt
Biotite
Plagioclase Feldspar
Rocks in the diorite family have an intermediate
composition that is neither felsic nor mafic, but has
characteristics of both. Their colors tend to be
medium gray and greens.
Properties
Color
Diorite
Andesite
Black, White, Gray with black
Salt and Pepper
crystals
Luster
Glassy
Glassy
Hardness
5.5 -6.5
6.5 - 7
Streak
Bluish black
White
Break
Cleavage
Conchoidal
Density
2.7 g/cm3
2.5 – 2.8 g/cm3
Specific Gravity
2.8 - 3
3.2 – 3.4
Crystal Structure
None
Orthorhombic
Special
Properties
-
Ultramafic rocks consist of mainly mafic minerals
that are dark in color, coarse grain and dense. Rocks
in this family include:
Peridotite
Dunite
Pyroxenite
Igneous intrusion occurs when magma forces its way
into fractures in the bedrock. The magma cools, leaving
a layer of igneous rock which is different than the
surrounding rock. Intrusion will only be revealed only
after overlaying has been eroded away or has been
uplifted.
Pluton: A large, thick igneous rock mass that
forms when magma cools within the
Earth’s interior.
Batholiths: The largest of all plutons. Batholiths
form the core of many of Earth’s
mountain ranges
Laccolith: A dome-shaped mass of intruded
igneous rock.
Dikes: Sheets of igneous rock that cut across rock layers
vertically or at steep angles.
Sills: Sheets of igneous rock that lie parallel to the
layers of rock it intrudes.
Volcanic Necks: The remains of a central vent of an
extinct volcano. These necks are only
revealed after all the surrounding
rock has been weathered and eroded
away.
Sedimentary rocks form through the compaction and
cementation of layers of sediment. The single most
characterizing feature of sedimentary rock is known as
“Stratification”. Stratification is a change in type of
sediment laid down resulting in the formation of a
new rock. Bedding planes are lines between each
different layer of sediment.
The process of forming a sedimentary rock is known as
“Lithification”. There are three main processes of
lithification:
Clastic Process
2. Chemical Process
3. Organic Process
1.
Clastic sedimentary rocks are formed from
fragments of other rocks. The process begins with
the movement and relocation of rock fragments
mainly by moving water. When the fragments
settle, (deposition), dissolved minerals, such as
silica, calcite, iron oxide, and clay, in the water fill
the empty spaces of the loose particles and cement
them together. This process is called “cementation”
Conglomerate
Breccia
Sandstone
Shale
Chemical rocks form with minerals dissolved in water
precipitate from solution. Precipitation can occur by
evaporation or chemical action.
Chemical action: While in solution, dissolved ions
combine to form new minerals. Examples of chemical
action are: Rock Salt, Halite, Gypsum, and Limestone
Organic sedimentary rock forms from sediment
containing the remains of plants and animals. Common
organic sedimentary rocks are limestone and coal.
Organically formed limestone contains the mineral
calcite. The process begins when water dissolves calcite
out of rocks on land and carries it in the form of ions to
lakes or oceans. Certain aquatic organisms, such as
clams, corals and some algae, use the ions to produce
calcium carbonate shells. When these organisms die,
their shells fall to the ocean floor and begin to pile up.
Over time, other minerals in the ocean cement the shells
together to form coquina.
Coquina is broken down into fragments by ocean waves
and these fragments are cemented together into
limestone.
Limestone formed near shore contain large amounts of
clay. Limestone that forms farther from shore are
almost pure calcite.
Peat
Bituminous
Lignite
Anthracite
Fossils: Fossils are the remains, impressions, and any
other evidence of plants or animals preserved
in rock.
Ripple marks are sand patterns formed by the action of
wind, streams, waves, or currents. Ripple marks can be
preserved when sand becomes sandstone.
Mud cracks develop when deposits of wet clay dry and
contract. The cracks fill in with different sediment and
fossilize when the clay become shale.
Limestone and chalk often contain hard lumps of fine
grained silica called nodules. Whitish, brown or gray
nodules are called chert. Darker varieties are sometimes
called flint. Throughout the ages, human have used
these nodules for tools and weapons.
Round solid masses of calcium carbonate that form in
layer of shale are called concretions. Concretions and
nodules form when minerals in solution precipitate
around a shell fragment or other impurity in clay
sediment.
Limestone sometimes contains spheres of silica rock
called geodes. Some geologist hypothesize that geodes
form when groundwater creates cavities in the
limestone. Minerals in the groundwater concentrate and
grow in the cavities.
Metamorphic rocks are formed from preexisting rocks
called “Parent Rocks”. The process by which a rock’s
structure is changed by pressure, heat, and moisture
is known as metamorphism. Rocks that undergo
metamorphism can have a different internal structure,
chemical composition, and texture than it’s parent rock.
Foliated metamorphic rock has tendency to form bands
of minerals or split along parallel layers. Non-foliated
metamorphic rocks tend to fracture.
Foliated
Non-Foliated
There are two main types of metamorphism:
Regional Metamorphism
2. Local Metamorphism
1.
Description of regional metamorphism:
Occurs during mountain building
2. Covers a large area
3. Exposure to high heat and pressure
4. When pressure is exerted greater in one
direction, the minerals in the rock tend to align
in layers.
1.
When compared to regional metamorphism, contact
metamorphism covers a much smaller area, usually
less than 100 meters.
There are two types of local metamorphism:
Contact Metamorphism
2. Deformational Metamorphism
1.
Contact metamorphism occurs when magma moves
into rock, heating and changing it. Contact
metamorphism fewer changes to the rock, in a much
small area.
Deformational metamorphism occurs at relatively
low temperature but high pressure caused by stress
and friction, most often at faults where rock masses
pass each other. As the rock masses move, heat from
friction, stress, and pressure cause the rock to
deform.
Sandstone
Shells
Quartzite
Limestone
Marble
Shale
Slate
Granite
Phyllite
Gneiss
Schist