Transcript Chapter Three

Chapter Three
ROCKS
Section 3-1 Classifying Rocks
• When studying a rock sample, geologists
observe the rock’s color and texture and
determine its mineral composition.
– Using color and texture, geologists can classify
a rock according to its origin.
– Texture is the look that results from the size,
shape, and pattern of the rocks grains.
3-1
• Coarse-grained: the grains are large and
easy to see.
• Fined-grained: the grains are small and can
been seen under a microscope or hand-lens.
– Some rock’s grains results from the shape of
the crystals that form the rock.
– In other rocks, the grain shapes result from
fragments of other rock.
Texture
Texture
3-1
• The three major groups of rock are:
– Igneous: forms from the cooling of molten
rock.
– Sedimentary: forms when particles of other
rocks of the remains of plants and animals are
pressed and cemented together.
– Metamorphic: forms when an existing rock is
changed by heat, pressure, or chemical
reactions.
3-2 Igneous Rock
• Igneous rock is any rock that forms from
magma or lava. Most igneous rocks are
made of mineral crystals. Igneous rocks are
classified according to their origin, texture,
and mineral composition.
Classification of Igneous Rock
Extrusive Rock
– Extrusive rock: is igneous rock formed
from lava that erupted onto Earth’s
surface.
• Basalt is the most common extrusive
rock.
Samples of Extrusive Rock
3-2
– Intrusive rock: Igneous rock that formed
when magma hardened beneath the
Earth’s surface.
• Granite is the most abundant intrusive
rock.
– The texture of an igneous rock depends
on the size and shape of its mineral
crystals.
• Texture may be fine-grained, coarse-grained,
porphyritic, or glassy.
– Fined-grained: rapid cooling lava forms
fined-grained.
– Coarse-grained: slow cooling lava forms
coarse-grained.
– Porphyritic: large crystals scattered on
top of small crystals. This occurs when
magma cools in two stages, first slow,
and then rapidly as magma moves near to
the surface.
Samples of Intrusive Rock
Granite
Samples of Intrusive Rock
Gabbros
Samples of Intrusive Rock
Diorite
3-2
• Lava low in silica forms dark-colored rocks,
such as basalt.
• Magma that is high in silica usually forms
light colored rocks, such as granite.
• Many igneous rocks are hard, dense, and
durable. People use igneous rock for tools
and building materials.
3-3 – Sedimentary Rock
•
Sedimentary rocks form from particles deposited by water and wind.
Sand, mud, and pebbles. Sediment is small, solid pieces of material
that come from rocks or living things.
1. Erosion: running water or wind loosen and carry
fragments of rock.
2. Deposition: the process by which sediment settles out
of the water or wind.
3. Compaction: the process that presses sediments
together.
4. Cementation: the process in which dissolved minerals
crystallize and glue particles of sediment together.
3-3
• There are three major groups of sedimentary rocks:
– Clastic rock: sedimentary rock that forms when rock fragments are
squeezed together. Sandstone is a clastic rock formed from the
compaction and cementation of sand.
– Organic Rock: forms where the remains of plants and animals are
deposited in thick layers. Coal is formed from the remains of
swamp plants and limestone is formed from the hard shells of
living things – seashells.
– Chemical Rock: when minerals that are dissolved in a solution
crystallize. Chemical rocks also form from mineral deposits left
when seas or lakes evaporate.
Samples of Sedimentary Rock
• Sandstone
Samples of Sedimentary Rock
• Gypsum
Samples of Sedimentary Rock
• Shale
3-4 Rocks from Reefs
• Coral animals are tiny relatives of jellyfish that live
together in vast numbers. They build skeletons that grow
together to form a structure called a coral reef.
• Coral reefs only form in warm, shallow tropical waters.
• When coral animals die, their skeletons remain, and new
corals build on top of them.
• There are three types of coral reefs: fringing reefs, barrier
reefs, and atolls.
• A coral reef is really organic limestone.
Fringing Reef
Barrier Reef
Atoll Reef
Coral Reefs
Coral Reefs
3-5 Metamorphic Rock
• Every metamorphic rock is a rock that has
changed its form. Heat and pressure deep beneath
Earth’s surface can change any rock into
metamorphic rock. Metamorphic rock can form
out of igneous, sedimentary, or other metamorphic
rock.
– Geologists classify metamorphic rocks by the
arrangement of the grains that make up the rocks.
• Metamorphic rocks that have their grains arranged in parallel
layers or bands are said to be foliated – slate is the most
common.
• Metamorphic rocks that have grains arranged randomly.
Marble and Quartz.
Metamorphic Rock Samples
Metamorphic Rock Samples
• Marble
Metamorphic Rock Sample
• Quartz
3-6 Rock Cycle
• Forces inside Earth and at the surface
produce a rock cycle that builds, destroys,
and changes the rocks in the crust.
– The rock cycle is a series of processes on and
beneath Earth’s surface that slowly change
rocks from one kind to another.
The Rock Cycle
Rock Pictures - Lava
• http://www.hoho.co.uk/html/lanzarote_lava
_and_rocks.html