Ch 5 Igneous Rocks What You NEED to

Ch 5, Igneous Rocks What You NEED to Know

Ch 5. 1 Objectives • Compare and contrast intrusive and extrusive igneous rocks. • Describe the composition of magma. • Discuss the factors that affect how rocks melt and crystallize. Vocabulary – igneous rock – partial melting – lava – fractional crystallization – extrusive – Bowen’s reaction series – intrusive

3 Kinds of Rocks • Igneous – made from the cooling of molten material • Sedimentary – made from the deposition and cementation of sediments • Metamorphic – made from the recrystalization of other rocks (because of heat and / or pressure)

The Rock Cycle

Igneous Rocks • Can be classified based on: –Method of deposition • Intrusive • Extrusive –Composition • Felsic (light colored minerals) • Mafic (dark colored minerals)

Intrusive vs. Extrusive • Intrusive cools slowly, under the surface –Large crystal size • Extrusive cools quickly, on the surface –Small crystal size

Intrusive vs. Extrusive Intrusive

Pegmatite – an intrusive igneous rock

Granite – an Intrusive Igneous Rock

Rhyolite – an Extrusive Igneous Rock

Obsidian – an extrusive igneous rock

Pegmatite Granite Intrusive Large crystals Rhyolite Obsidian Extrusive Small crystals

Origins of Magma Factors That Affect Magma Formation – Granite’s higher water content and mineral composition cause it to melt at a lower temperature than basalt.

How Rocks Melt Partial Melting – Because different minerals have different melting points, not all parts of a rock melt at the same time. – Partial melting is the process whereby some minerals melt at low temperatures while other minerals remain solid.

How Rocks Melt Partial Melting – If temperatures are not great enough to melt the entire rock, the resulting magma will have a different chemistry from that of the original rock. – This is one way in which different types of igneous rocks form.

How Rocks Melt Fractional Crystallization – When magma cools, it crystallizes in the reverse order of partial melting—the first minerals to crystallize from magma are the last minerals to melt during partial melting. – Fractional crystallization is the process wherein different minerals form at different temperatures.

Bowen’s Reaction Series • Bowen’s reaction series illustrates the relationship between cooling magma and mineral formation. • Bowen discovered two main patterns, or branches, of crystallization. – The first pattern is characterized by a continuous, gradual change of mineral compositions in the feldspar group. – The second pattern is characterized by an abrupt change of mineral type in the ironmagnesium groups.

Bowen’s Reaction Series

Bowen’s Reaction Series

Ch 5 -2 Objectives • Classify different types and textures of igneous rocks. • Recognize the effects of cooling rates on the grain sizes of igneous rocks. • Describe some uses of igneous rocks. Vocabulary – felsic – pegmatite – mafic – kimberlite – ultramafic – porphyritic

Composition • Felsic Rock –mostly light colored, silicate minerals –Low melting point • Mafic Rock –Mostly dark colored, iron & magnesium rich silicates –High melting point

Granite – an Felsic Rock

Diorite – an Intermediate Rock (between Felsic & Mafic)

Basalt – A Mafic Rock

Peridotite (Kimberlite)– an Ultramafic Rock

Felsic light colored minerals Granite Diorite Basalt Mafic Dark colored minerals Peridotite

Rhyolite? Intrusive or Extrusive? Extrusive Composition? Felsic

Gabbro? Intrusive or Extrusive? Intrusive Composition? Mafic

Diorite? Intrusive or Extrusive? Intrusive Composition? Intermediate

Andesite? Intrusive or Extrusive? Extrusive Composition? Intermediate

Felsic Pegmatite Granite Diorite Gabbro Mafic Peridotite Intrusive Rhyolite Obsidian Andesite Basaltic Glass Extrusive