Download Intrusive igneous rock

Rocks
Introduction
• Elements are chemically combined to
form minerals
• Minerals are physically combined to
form rocks.
• There are 3 categories of rocks: igneous,
metamorphic and sedimentary
Igneous rocks
• Form from the cooling of molten rock material
• Two main types:
• Intrusive igneous rock
• Formed when magma cools deep within the
Earth’s surface
• Cools very slowly as it is in contact with molten
rock.
• Produces course-grained igneous rock.
• Extrusive igneous rock
• Magma that cools above the Earth’s surface.
• Produces fine-grained igneous rocks.
• This rapid cooling does not allow time for crystals
to form.
• Igneous rock classification scheme is based on
mineral composition and texture (coarse or fine
grained). There are other blends of minerals
with various textures, many of which have
specific names.
• Granite is a coarse-grained igneous rock
composed mostly of light-colored, light-density,
non-ferromagnesian (big fancy word for rock
not having iron) minerals. The earth's
continental areas are dominated by granite and
by rocks with the same mineral composition of
granite.
• This is a piece of obsidian, which has the
same chemical composition as the granite.
Obsidian has a different texture (cooled
really fast) because it does not have crystals
and is a volcanic glass.
• Basalt is a fine-grained igneous rock
composed mostly of dark-colored, heavydensity, ferromagnesian (big fancy word for
rock with iron) minerals. The earth's oceanic
areas are dominated by basalt and similar
rocks.
Sedimentary Rocks
• Form from material from previously
existing rock
• Material is provided by weathering of
previously existing rock
• Type of sedimentary rock is determined by
the parent rock, the rock that was weathered
originally
• Sediments
• Weathered rock materials
• Dissolved rock materials
• This is a sample of breccia, a coarse-grained
sedimentary rock with coarse, angular
fragments. Compare the grain sizes to the
centimeter scale. Common in sites of
landslides and little water.
• A conglomerate is similar to breccia in that it is a
mixture of rock sediments, but the larger fragments
are rounded because they were eroded by water.
Usually these are found near a lake or a stream or
where one use to be.
• This is a sample of sandstone, a sedimentary
rock that formed from sand grains in a matrix of
very fine-grained silt, clay, or other materials.
The grains in this sample are mostly the
feldspar and quartz minerals, which probably
accumulated near the granite from which they
were eroded.
Chemical Sedimentary Rocks
• Chemical sediments
• Another name for dissolved rock material.
• The dissolved materials are ions from mineral
and rocks that have been completely broken
down.
• Removed from solution by:
• Chemical precipitation from the solution
• Crystallization from evaporating water.
• Biological sediments.
• This is a sample of limestone, a sedimentary
rock made of calcium carbonate that formed
under water directly or indirectly from the
actions of plants and animals. This finegrained limestone formed indirectly from
the remains of tiny marine organisms.
• Coquina. Form of limestone produced through the
accumulation of old shells from sea creatures
Process of Making Sedimentary
Rock
• Compaction
• As sediments are laid down grain by grain, the mass
becomes greater.
• The increasing mass of the sediment layer above
creates pressure on the layers below.
• Eventually this pressure becomes great enough to
compact the existing layers into a cohesive rock
layer.
• Cementation
• When spaces between the sediment particles
become filled with a chemical deposit.
• This deposit holds the compacted layers into a
cohesive mass of sedimentary rock.
• (A)In compaction, the
sediment grains are
packed more tightly
together, often by
overlying sediments,
as represented by the
bricks.
• (B) In cementation,
fluids contain
dissolved minerals
that are precipitated
in the space between
the grains, cementing
them together into a
rigid, solid mass.
Metamorphic Rocks
• Rocks changed by heat, pressure, or hot solutions
due to:
• Movement of the Earth’s crust
• Heat generated by intrusion of hot magma
• Pressure can change rock by flattening, deforming, or
realigning mineral grains.
• Foliation
• When the pressure on flat crystal flakes tends to align
the flakes into parallel sheets.
• Gives the rock the property of breaking along the planes
between the aligned mineral grains in what is known as
rock cleavage.
• Increasing metamorphic change occurs with
increasing temperatures and pressures. If the
melting point is reached, the change is no
longer metamorphic, and igneous rocks are
formed.
• This is a sample of marble, a coarse-grained
metamorphic rock with interlocking calcite
crystals. The calcite crystals were
recrystallized from limestone during
metamorphism.
• This banded
metamorphic rock is
very old; at an age of
3.8 billion years, it is
probably among the
oldest rocks on the
surface of the earth.
The Rock Cycle
• Earth is a dynamic planet with the
surface and interior in a constant state of
flux/change.
• Internal changes alter the surface by
moving the Earth’s plates, building
mountains.
• Seas advance and retreat over the
continents brining in new materials and
taking other materials away.
• Rocks are continually being changed by
Earth’s forces.
• The Rock Cycle describes the
continually changing structure of
rocks.
• Igneous, sedimentary, or
metamorphic rock are just
temporary stages in the continuing
changes that all rocks undergo.
• A schematic diagram of the rock cycle concept,
which states that geologic processes act
continuously to produce new rocks from old
ones.