IGNEOUS ROCKS BEGIN
WHAT IS AN IGNEOUS ROCK? An igneous rock is a rock that has formed from the cooling and solidification of magma or lava. LAST
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MAGMA
LAVA
Melted rock that is beneath the surface of the Earth.
Melted rock that is at or near the surface of the Earth.
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Lava Magma LAST
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TYPES OF IGNEOUS ROCKS Igneous rocks are classified according to where they cooled and solidified.
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INTRUSIVE IGNEOUS ROCKS
EXTRUSIVE IGNEOUS ROCKS
Rocks that form from magma cooling and solidifying while still inside the Earth
Rocks that form from lava cooling and solidifying while at or near the Earth
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P. 6 of ESRT LAST
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Vesicular rhyolite
Vesicular andesite
noncrystalline
Scoria Vesicular basalt
Andesite
Basalt Diabase
Granite
FELSIC (rich in Si, Al)
75%
DARKER
DENSITY
HIGHER
Glassy
Nonvesicular Vesicular (gas pockets)
Fine
Coarse
Nonvesicular
Very coarse
100%
Potassium feldspar (pink to white) Quartz (clear to white)
TEXTURE
MAFIC (rich in Fe, Mg)
COMPOSITION
75% Plagioclase feldspar (white to gray)
Biotite (black) Amphibole (black)
0%
Gabbro
COLOR
50%
25%
Peridotite
Pegmatite
LOWER
100%
Diorite
CRYSTAL SIZE
10 mm 1 mm less than or to 1 mm larger 10 mm
Pumice
Dunite
EXTRUSIVE (Volcanic)
Basaltic glass
LIGHTER
MINERAL COMPOSITION (relative by volume)
CHARACTERISTICS
INTRUSIVE
Obsidian (usually appears black)
Rhyolite
INTRUSIVE (Plutonic)
IGNEOUS ROCKS
EXTRUSIVE
ENVIRONMENT OF FORMATION
Scheme for Igneous Rock Identification
50%
Pyroxene (green) Olivine (green)
25%
0%
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Physical Setting/Earth Science Reference Tables — 2010
INTRUSIVE IGNEOUS ROCKS Because these rocks form inside the Earth, where it is very hot, it takes a long time for the magma to cool and solidify. This time allows mineral crystals to grow large. So all intrusive igneous rocks have inter-grown crystals that are larger than 1mm. LAST
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INTRUSIVE IGNEOUS ROCKS
PEGMATITE
GRANITE
*Notice the large mineral crystals LAST
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Pumice
Scoria
noncrystalline
Basaltic glass
Vesicular andesite
Vesicular rhyolite
Vesicular basalt
Andesite
Basalt
Diabase Diorite
Granite Pegmatite
Environment of Formation LOWER (where the rock formed)
FELSIC ch in Si, Al)
DENSITY
P. 6 of ESRT
Coarse
Nonvesicular
Very coarse
(description of crystal 100% sizes) Non-vesicular means these rocks do 75% not have any trapped air bubbles
Plagioclase feldspar (white to gray)
50%
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Fine
MAFIC Texture (rich in Fe, Mg)
COMPOSITION
(pink to white)
Quartz (clear to white)
Vesicular (gas pockets)
Range of crystal sizes HIGHER
Names of common Potassium intrusive igneous rocks feldspar
75%
Glassy
Nonvesicular
DARKER
COLOR
LIGHTER
100%
Gabbro
Peridotite
10 mm 1 mm less than or to 1 mm larger 10 mm
INTRUSIVE IGNEOUS ROCKS Dunite
EXTRUSIVE (Volcanic)
Obsidian (usually appears black)
Rhyolite
INTRUSIVE (Plutonic)
ENVIRONMENT OF FORMATION
SIZE
Biotite (black)
Pyroxene (green)
50%
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EXTRUSIVE IGNEOUS ROCKS Because these rocks form on or near the surface of the Earth, where temperatures are lower, the lava cools and solidifies quickly. Without time, crystals cannot grow very large, or may not even form at all. So all extrusive igneous rocks have either no crystals, or crystals that are smaller than 1mm. LAST
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EXTRUSIVE IGNEOUS ROCKS
BASALT
RHYOLITE
*Notice the mineral crystals are so small, you can barely see them LAST
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EXTRUSIVE IGNEOUS ROCKS
BASALTIC GLASS
OBSIDIAN
*These extrusive igneous rocks formed so quickly, no crystals were able to form. They are called “glassy” or “non-crystalline.” LAST
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STREAM VELOCITY (cm/s) This generalized graph shows the water velocity needed to maintain, but not start, movement. Variations occur due to differences in particle density and shape.
EXTRUSIVE IGNEOUS ROCKS Scoria Vesicular andesite
Vesicular rhyolite
Andesite
noncrystalline
Pumice
Vesicular basalt Basalt Diabase
Diorite
Granite
Environment of Formation Pegmatite (where the rock formed)
LIGHTER
P. 6 of ESRT 100%
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COLOR DENSITY
FELSIC ich in Si, Al)
Potassium feldspar (pink to white)
Peridotite
Range of crystal sizes
Names of common intrusive igneous rocks
LOWER
Gabbro
CRYSTAL SIZE
10 mm 1 mm less than or to 1 mm larger 10 mm
Basaltic glass
Dunite
EXTRUSIVE (Volcanic)
Obsidian (usually appears black)
Rhyolite INTRUSIVE (Plutonic)
ENVIRONMENT OF FORMATION
Scheme for Igneous Rock Identification
COMPOSITION
TEXTURE
Glassy
Nonvesicular Vesicular (gas pockets)
Fine
Coarse
Nonvesicular
Very coarse
Texture (description of crystal DARKER sizes) HIGHER
Some of these rocks have trapped gas MAFIC (rich in Fe, Mg)do not bubbles, some 100%
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A quick review... ✓
Igneous rocks form from cooled and solidified magma or lava.
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When magma cools slowly inside Earth, we get intrusive (plutonic) igneous rocks with large crystals.
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When lava cools quickly at or near Earth’s surface, we get extrusive (volcanic) igneous rocks with small or no crystals. These may be vesicular, meaning there are trapped gas bubbles.
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Page 6 of the ESRT shows common igneous rocks and their characteristics.
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6
Vesicular rhyolite
Vesicular andesite
noncrystalline
Scoria Vesicular basalt
Andesite
Basalt Diabase
Granite
FELSIC (rich in Si, Al)
75%
DARKER
DENSITY
HIGHER
Glassy
Nonvesicular Vesicular (gas pockets)
Fine
Coarse
Nonvesicular
Very coarse
100%
Potassium feldspar (pink to white) Quartz (clear to white)
TEXTURE
MAFIC (rich in Fe, Mg)
COMPOSITION
75% Plagioclase feldspar (white to gray)
Biotite (black) Amphibole (black)
0%
Gabbro
COLOR
50%
25%
Peridotite
Pegmatite
LOWER
100%
Diorite
CRYSTAL SIZE
10 mm 1 mm less than or to 1 mm larger 10 mm
Pumice
Dunite
EXTRUSIVE (Volcanic)
Basaltic glass
Rhyolite INTRUSIVE (Plutonic)
ENVIRONMENT OF FORMATION
IGNEOUS ROCKS CHARACTERISTICS
Obsidian (usually appears black)
LIGHTER
MINERAL COMPOSITION (relative by volume)
IGNEOUS ROCK COLORS
Scheme for Igneous Rock Identification
50%
Pyroxene (green) Olivine (green)
25%
0%
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Physical Setting/Earth Science Reference Tables — 2
6
Vesicular rhyolite
Vesicular andesite
noncrystalline
Scoria Vesicular basalt
Andesite
Basalt Diabase
Granite
FELSIC (rich in Si, Al)
75%
DARKER
DENSITY
HIGHER
Glassy
Nonvesicular Vesicular (gas pockets)
Fine
Coarse
Nonvesicular
Very coarse
100%
Potassium feldspar (pink to white) Quartz (clear to white)
TEXTURE
MAFIC (rich in Fe, Mg)
COMPOSITION
75% Plagioclase feldspar (white to gray)
Biotite (black) Amphibole (black)
0%
Gabbro
COLOR
50%
25%
Peridotite
Pegmatite
LOWER
100%
Diorite
CRYSTAL SIZE
10 mm 1 mm less than or to 1 mm larger 10 mm
Pumice
Dunite
EXTRUSIVE (Volcanic)
Basaltic glass
Rhyolite INTRUSIVE (Plutonic)
ENVIRONMENT OF FORMATION
IGNEOUS ROCKS CHARACTERISTICS
Obsidian (usually appears black)
LIGHTER
MINERAL COMPOSITION (relative by volume)
IGNEOUS ROCK DENSITY LAST
Scheme for Igneous Rock Identification
50%
Pyroxene (green) Olivine (green)
25%
0%
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Physical Setting/Earth Science Reference Tables — 2
6
Vesicular rhyolite
Vesicular andesite
noncrystalline
Scoria Vesicular basalt
Andesite
Basalt Diabase
Granite
FELSIC (rich in Si, Al)
75%
DARKER
DENSITY
HIGHER
Glassy
Nonvesicular Vesicular (gas pockets)
Fine
Coarse
Nonvesicular
Very coarse
100%
Potassium feldspar (pink to white) Quartz (clear to white)
TEXTURE
MAFIC (rich in Fe, Mg)
COMPOSITION
75% Plagioclase feldspar (white to gray)
Biotite (black) Amphibole (black)
0%
Gabbro
COLOR
50%
25%
Peridotite
Pegmatite
LOWER
100%
Diorite
CRYSTAL SIZE
10 mm 1 mm less than or to 1 mm larger 10 mm
Pumice
Dunite
EXTRUSIVE (Volcanic)
Basaltic glass
Rhyolite INTRUSIVE (Plutonic)
ENVIRONMENT OF FORMATION
IGNEOUS ROCKS CHARACTERISTICS
Obsidian (usually appears black)
LIGHTER
MINERAL COMPOSITION (relative by volume)
IGNEOUS ROCK COMPOSITION LAST
Scheme for Igneous Rock Identification
50%
Pyroxene (green) Olivine (green)
25%
0%
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Physical Setting/Earth Science Reference Tables — 2
IGNEOUS ROCK MINERALS
This generalized graph shows the water velocity needed to maintain, but not start, movement. Variations occur due to differences in particle density and shape.
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Find the rock name and look below it to see what minerals may be present in that rock. Scheme for Igneous Rock Identification Vesicular rhyolite
Vesicular andesite
noncrystalline
Scoria Vesicular basalt
Andesite
Basalt
INTRUSIVE (Plutonic)
Diabase Granite
FELSIC (rich in Si, Al)
75%
Gabbro
COLOR
DARKER
DENSITY
HIGHER
Glassy
Nonvesicular Vesicular (gas pockets)
Fine
Coarse
Nonvesicular
Very coarse
100%
Potassium feldspar (pink to white) Quartz (clear to white)
TEXTURE
MAFIC (rich in Fe, Mg)
COMPOSITION
75% Plagioclase feldspar (white to gray)
50%
25%
Peridotite
Pegmatite
LOWER
100%
Diorite
10 mm 1 mm less than or to 1 mm larger 10 mm
Pumice
Dunite
EXTRUSIVE (Volcanic)
Basaltic glass
Rhyolite
Biotite (black) Amphibole (black)
0%
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Obsidian (usually appears black)
LIGHTER
MINERAL COMPOSITION (relative by volume)
CHARACTERISTICS
IGNEOUS ROCKS
ENVIRONMENT OF FORMATION
CRYSTAL SIZE
50%
Pyroxene (green) Olivine (green)
25%
0%
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Physical Setting/Earth Science Reference Tables — 2010
