Module 2.2: Rocks (Igneous)

Rock

A naturally-occurring aggregate of one or more minerals, rock fragments, glass, or organic matter

Igneous rocks

Formed by cooling and crystallization of molten material called magma

Magma

A mobile, molten rock beneath the Earth’s surface that originates from the partial melting of the oceanic crust and/or the upper mantle

Silicate (sometimes carbonate or sulfide) and ions of K, Na, Fe, Ca, Mg, & Al

These are the liquid components of magma.

Minerals and rock fragments

These are the solid components of magma.

Water (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2)

These are the dissolved gases found in magma.

600-1200 °C

Temperature range for magma

Viscosity

It is the property of a liquid to resist flow.

Lower viscosity

Effect of higher temperature on viscosity

Higher viscosity

Effect of high silica/silicon dioxide content on viscosity

Lower viscosity

Effect of high dissolved water on viscosity

Felscic/silicic/acidic (>63% SiO2)

• Type of magma formed from continental crust

• Characterized by lowest temperature and density, but highest silica content (also identify percent) and viscosity

Intermediate (52-63% SiO2)

• Type of magma formed from continental crust

• Characterized by low temperature and density, but high silica content (also identify percent) and viscosity

Mafic/basic (45-52% SiO2)

• Type of magma formed from oceanic crust

• Characterized by high temperature and density, but low silica content (also identify percent) and viscosity

Ultramafic/ultrabasic (<45% SiO2)

• Type of magma formed from the upper mantle

• Characterized by highest temperature and density, but lowest silica content (also identify percent) and viscosity

Extrusive/volcanic

Type of igneous rocks solidifed at the surface forming finer crystals

Intrusive/plutonic

Type of igneous rocks formed at depth in chambers forming large crystals

Euhedral

Mineral grains are bounded by its crystal faces on all sides

Subhedral

Mineral grains are partly bounded by its crystal faces

Anhedral

Mineral grains are not bounded by its crystal faces

Aphanitic

• Texture of igneous rocks with very fine-grained (<2mm in diameter) as a result of rapid cooling at the surface

• Have minerals too small to be seen by the naked eye

Phaneritic

Texture of igneous rocks with coarse-grained (>5mm) mineral sizes due to magma cooling at depth

Porphyritic

Texture of igneous rocks with very large crystals embedded in smaller crystals

Phenocrysts

Very large crystals embedded in smaller crystals formed in porphyritic igneous rocks

Groundmass

Smaller crystals formed in porphyritic igneous rocks

Vesicular

Texture of igneous rocks containing tiny holes called vesicles formed due to gas bubbles in the lava or magma

Glassy

Texture of igneous rocks with no mineral grains due to molten rock being quenched quickly as it was ejected into the atmosphere

Pyroclastic

Texture of igneous rocks made of rock fragments rather than crystals due to volcanic materials being extruded violently

Equigranular

Texture of igneous rocks with minerals that are uniform in size

Bowen’s Reaction Series

Describes the sequence in which minerals crystallize from cooling magma

Granite (phaneritic, felsic)

Identify the igneous rock, its texture, and composition

Granite (phaneritic, felsic)

Identify the igneous rock, its texture, and composition

Diorite (phaneritic, intermediate)

Identify the igneous rock, its texture, and composition

Diorite (phaneritic, intermediate)

Identify the igneous rock, its texture, and composition

Gabbro (phaneritic, mafic)

Identify the igneous rock, its texture, and composition

Gabbro (phaneritic, mafic)

Identify the igneous rock, its texture, and composition

Rhyolite (aphanitic, felsic)

Identify the igneous rock, its texture, and composition

Rhyolite (aphanitic, felsic)

Identify the igneous rock, its texture, and composition

Andesite (aphanitic, intermediate)

Identify the igneous rock, its texture, and composition

Andesite (aphanitic, intermediate)

Identify the igneous rock, its texture, and composition

Basalt (aphanitic, mafic)

Identify the igneous rock, its texture, and composition

Basalt (aphanitic, mafic)

Identify the igneous rock, its texture, and composition

Rhyolite (porphyritic, felsic)

Identify the igneous rock, its texture, and composition

Andesite (porphyritic, intermediate)

Identify the igneous rock, its texture, and composition

Basalt (porphyritic, mafic)

Identify the igneous rock, its texture, and composition

Pumice

Identify the igneous rock

Scoria

Identify the igneous rock

Vesicular basalt

Identify the igneous rock

Tuff

Identify the igneous rock

Obsidian

Identify the igneous rock

Ignimbrite

Identify the igneous rock

Peridotite (phaneritic, ultramafic)

Identify the igneous rock, its texture, and composition

Komatiite (aphanitic, ultramafic)

Identify the igneous rock, its texture, and composition