Igneous rocks armetta
Transcript of Igneous rocks armetta
ROCKS:
You probably don’t realize it,
but we depend on many rocks in our everyday lives. Rocks have different
chemical and physical properties that make them quite useful to us. Besides providing a
nice hard place for us to stand on Earth, we use rocks for the construction of our homes, for fuel, and for the creation of statues and art. Go home today and look around your house. You may be
surprised by what rocks you find.
ROCKS:
A ROCK is composed of one or more minerals. Rocks composed of only
one mineral are said to be MONOMINERALLIC.
This is a photo of a slice of Dunite, a monominerallic igneous
rock, under a microscope. Almost all of the grains in this rock are olivine. Note the high
order interference colors of olivine and the minor secondary calcite which occurs as veinlets
through the sample.
ROCKS: Most rocks are POLYMINERALLIC, that is, made of many different minerals. There are over 2,500 different minerals. However, there are 10-15 minerals known as the
rock-forming minerals, which compose about 90% of all the rocks in Earth’s crust.
METHOD OF FORMATION:
Rocks are classified by their METHOD OF FORMATION, into
three groups:
1) IGNEOUS2) SEDIMENTARY3) METAMORPHIC
Let’s take a more detailed at each.
IGNEOUS ROCKS:
Igneous rocks form from the MELTING and SOLIDIFICATION (hardening) of
molten material from within the Earth.
IGNEOUS ROCKS:Molten material within the Earth is
called MAGMA. When this molten material reaches Earth’s surface it’s
called LAVA. LAVA:
ON OR NEAR EARTH’S SURFACE
MAGMA:INSIDE OF
EARTH
IGNEOUS ROCKS:
Igneous rocks are solid, hard, and compact and are composed of randomly arranged
INTERGROWN MINERAL CRYSTALS.
GRANITE IS AN IGNEOUS ROCK WITH COARSE GRAINED CRYSTALS.
MAYBE YOU CAN SEE THEM BETTER CLOSE
UP?
TEXTURE:
Igneous rocks are best identified by their texture, environment of
formation, and mineral composition
Texture describes a rock’s “grain appearance” which is determined by
the size of the crystal and the arrangement of the crystals.
There are FOUR textures: glassy, fine, coarse, and very coarse.
TEXTURE:
1) GLASSY: A glassy texture forms when a mineral cools so quickly that no crystals are visible. Glassy textures occur when there is a rapid drop in
temperature and pressure. This condition exists when magma reaches Earth’s surface through a volcano.
OBSIDIAN
SCHEME FOR IGNEOUS ROCK IDENTIFICATIONIN YOUR ESRT:
TEXTURE:
There are TWO types of glassy texture:
a) VESICULAR: A vesicular texture exhibits gas pockets and the rock appears holey. Ex: Pumice
b) NON-VESICULAR: A non-vesicular texture looks like glass. Ex: Obsidian
PUMICE
OBSIDIAN
SCHEME FOR IGNEOUS ROCK IDENTIFICATIONIN YOUR ESRT:
TEXTURE:
2) FINE: A fine texture
forms when a mineral cools quickly at or near Earth’s surface. The grain size is less than 1mm. Ex: Rhyolite
RHYOLITE
SCORIABASALT
ANDESITE
SCHEME FOR IGNEOUS ROCK IDENTIFICATIONIN YOUR ESRT:
TEXTURE:
3) COARSE: A fine texture
forms when a mineral cools SLOWLY WITHIN the Earth under high pressure. The grain size ranges from 1-10 mm. Ex: Granite
GRANITE
DIORITE GABBROPERIDOITE
SCHEME FOR IGNEOUS ROCK IDENTIFICATIONIN YOUR ESRT:
TEXTURE:
4) VERY COARSE: A course
texture forms when a mineral cools very slowly within the Earth, producing grain sizes 10 mm or larger. Ex: Pegmatite
PEGMATITE
A CLOSER LOOK!!!
SCHEME FOR IGNEOUS ROCK IDENTIFICATIONIN YOUR ESRT:
TEXTURE:
TEXTURE IS DETERMINED BY THE
LENGTH OF COOLING!
Rocks that cool FAST have SMALLER crystals.
Rocks that cool SLOW have LARGER crystals.
SMALL CRYSTALS
COOLED FAST
LARGE CRYSTALS
COOLED SLOWLY
RATE & DEPTH OF COOLING:
SUPER IMPORTANT FACT!
The grain size of igneous rocks depends on the RATE and DEPTH at which magma cools.
The diagram shows the
relationship between grain
size and rate/depth of
cooling.
Basalt 0.1 mm
Diabase 1 mm
Granite 10 mm
ROCK NAME GRAIN SIZE ENVIRONMENT
Surface
Near Surface
Deep
Slow Moderate Fast COOLING RATE
A
B
C
RATE & DEPTH OF COOLING:
COOLING RATE COOLING TIME DEPTH
CR
YS
TA
L S
IZE
CR
YS
TA
L S
IZE
CR
YS
TA
L S
IZE
THESE ARE GRAPHING RELATIONSHIPS THAT YOU SHOULD KNOW.
RATE & DEPTH OF COOLING:
COOLING RATE COOLING TIME DEPTH
CR
YS
TA
L S
IZE
CR
YS
TA
L S
IZE
CR
YS
TA
L S
IZE
THESE ARE GRAPHING RELATIONSHIPS THAT YOU SHOULD KNOW.
ENVIRONMENT OF FORMATION:
By studying a rock’s texture, you can infer a rock’s environment of formation. There are TWO different environments of formation.
1) EXTRUSIVE or VOLCANIC: This is when an igneous rock hardens NEAR the Earth’s surface or ON the Earth’s surface to form a rock with small or no crystals. These rocks are found by volcanoes.
SCHEME FOR IGNEOUS ROCK IDENTIFICATIONIN YOUR ESRT:
ENVIRONMENT OF FORMATION:
2) INTRUSIVE or PLUTONIC: This is when
an igneous rock hardens within the Earth to form large crystals. When magma doesn’t erupt it can flow underground. Underground magma flows are called INTRUSIONS because they can move into and through fractures (cracks) in rock. If an intrusion hardens, it produces a large mass of igneous rock called a PLUTON.
SCHEME FOR IGNEOUS ROCK IDENTIFICATIONIN YOUR ESRT:
CHEMICAL COMPOSITION:
A rock’s chemical composition refers to a rock’s mineral make-up. Igneous rocks are generally
described as having either a FELSIC composition or a MAFIC composition.
1) FELSIC COMPOSITION: Rocks with a felsic composition tend to contain a high percentage of the minerals potassium feldspar and quartz. They are RICH IN ALUMINUM (Al) and low in both iron (Fe) and magnesium (Mg). These rocks are usually LIGHTER IN COLOR and LOWER IN DENSITY than mafic rocks. Felsic rocks make up a large portion of continental crust. The granite family of rocks is felsic.
SCHEME FOR IGNEOUS ROCK IDENTIFICATIONIN YOUR ESRT:
NOTE: Even
though OBSIDIAN is dark in color, it is considered FELSIC, because it is low in density.
This is the one
exception to the rule!
CHEMICAL COMPOSITION:
2) MAFIC COMPOSITION: Rocks with a mafic composition tend to contain a high percentage of the minerals plagioclase feldspar and pyroxene. They are RICH IN IRON (Fe) and MAGNESIUM (Mg) and low in ALUMINUM (Al). These rocks are usually DARKER IN COLOR and HIGHER IN DENSITY than felsic rocks. Mafic rocks are most common in the ocean basins. The Gabbro family of rocks is mafic.
SCHEME FOR IGNEOUS ROCK IDENTIFICATIONIN YOUR ESRT:
MINERAL COMPOSITION: WHAT IS MINERAL
COMPOSITION?Mineral composition
refers to the different minerals that a rock is
made up of and the percentages of these
minerals.
Granite is mostly made up of POTASSIUM
FELDSPAR (pink/gray), BIOTITE MICA (black),
and QUARTZ (clear/white).
MINERAL COMPOSITION:
SCHEME FOR IGNEOUS ROCK IDENTIFICATIONIN YOUR ESRT:
FINDING THE MINERAL COMPOSITION USING YOUR ESRT:
You can determine the possible mineral
composition of specific igneous
rocks by looking at your ESRT. Simply
find a rock name on the chart, then look
at the minerals found in the column
under that rock name. Your rock
name can contain varying amounts of
those materials.
FINDING THE PERCENTAGE OF MINERALS IN AN IGNEOUS ROCK USING YOUR ESRT:
You can determine the possible mineral
composition of specific igneous
rocks by looking at your ESRT. Simply
find a rock name on the chart, then look
at the minerals found in the column
under that rock name. Your rock
name can contain varying amounts of
those materials.
FINDING THE PERCENTAGE OF MINERALS IN AN IGNEOUS ROCK USING YOUR ESRT:
You can determine the possible mineral
composition of specific igneous
rocks by looking at your ESRT. Simply
find a rock name on the chart, then look
at the minerals found in the column
under that rock name. Your rock
name can contain varying amounts of
those materials.
REVIEW OF IGNEOUS ROCKS:INTRUSIVE
( PLUTONIC)EXTRUSIVE(VOLCANIC)
OBSIDIAN, SCORIA, PUMICE, RHYOLITE, ANDESITE, BASALT
FINE, GLASSY
SMALL
FAST
ON/NEAR EARTH’S SURFACE
GRANITE, DIORITE, GABBRO, PERIDOITE, DUNITE, PEGMATITE
COARSE, VERY COARSE
LARGE
SLOW
INSIDE EARTH ENVIRONMENT OF
FORMATION
SPEED OF COOLING
SIZE OF CRYSTAL
NAME OF TEXTURE
ROCK EXAMPLES
REVIEW OF IGNEOUS ROCKS:
FELSIC MAFIC
Scoria, Basalt, Gabbro, Peridoite,
Dunite
High
High
Dark
Iron (Fe)Magnesium (Mg)
Granite, Pegmatite, Rhyolite, Pumice,
Obsidian
Low
Low
Light
Aluminum (Al)Silicon (Si)
MINERAL COMPOSITION
COLOR
DENSITY
TEMPERATURE AT WHICH MINERALS
IN ROCK CRYSTALLIZE
ROCK EXAMPLES