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 NEXT MAGMA LAVA Melted rock that is beneath the surface of the Earth. Melted rock that is at or near the surface of the Earth. LAST NEXT Lava Magma LAST NEXT LAST NEXT LAST NEXT TYPES OF IGNEOUS ROCKS Igneous rocks are classified according to where they cooled and solidified. LAST NEXT LAST 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 NEXT P. 6 of ESRT LAST 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 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% NEXT 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 NEXT INTRUSIVE IGNEOUS ROCKS PEGMATITE GRANITE *Notice the large mineral crystals LAST NEXT 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% LAST 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% NEXT 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 NEXT EXTRUSIVE IGNEOUS ROCKS BASALT RHYOLITE *Notice the mineral crystals are so small, you can barely see them LAST NEXT 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 NEXT 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% LAST 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% NEXT A quick review... ✓ Igneous rocks form from cooled and solidified magma or lava. ✓ When magma cools slowly inside Earth, we get intrusive (plutonic) igneous rocks with large crystals. ✓ 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. ✓ Page 6 of the ESRT shows common igneous rocks and their characteristics. LAST NEXT LAST 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% NEXT 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% NEXT 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% NEXT 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. LAST 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% 6 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% NEXT Physical Setting/Earth Science Reference Tables — 2010