Important Economic Minerals Elements: Gold, Copper, Zinc… Sulfur Diamond, Graphite, Iron Oxides: Hematite (Fe 2 O 3 ), Magnetite (Fe 3 O 4 ) Elements and Ores Usually concentrated by biological or hydrothermal processes Associated with volcanism (plutonics) or metamorphism

Rock-Forming Minerals Sediments and Sedimentary Rocks Oxides (e.g., Iron oxides) Fe 2 O 3, Fe 3 O 4 Halides (e.g., with Cl - or S -2 ) NaCl, FeS 2 Sulfates (SO 4 ) -2 and Carbonates (CO 3 ) -2 FeSO 4, CaSO 4, CaSO 4,·(2H 2 O) CaCO 3, CaMg(CO 3 ) 2,

Fig. 2.9 From bottom to top Increasing Fe/Mg/Ca Decreasing silica Increasing density Darker minerals Decreasing Silica 29% 14% <20% 20% <3% 23% <2% 25% (0) 33% (0) 23% (0) 15%* % of Tot. # of atoms Fe/Mg: Silicon: Increasing Fe/Mg/Ca Quartz K and Na Feldspar Ca Feldspar Systematic Silicate Mineralogy Increasing Density Olivine Pyroxene Group Amphibole Group Mica Group

Fig. 2.9 From bottom to top Increasing Fe/Mg/Ca Decreasing silica Increasing density Darker minerals Fe/Mg/Ca Content Density Susceptibility to Weathering* Quartz K and Na Feldspar Ca Feldspar # Systematic Silicate Mineralogy and Engineering Properties Olivine Pyroxene Group Amphibole Group Mica Group Melting and crystallizing Temperature ~ Increasing Decreasing *All of these silicates weather to form Clay Minerals Except quartz ~ Quartz melts first Mantle Oceanic Crust # Cont. Crust

Minerals in sediment Sandy and clayey soils Quartz Na Plagioclase Quartz Feldspar Clay Calcite Hematite Sediments of: Rocks (at surface) Sediment Weathered to form Biotite

Minerals in Rocks Clastic sedimentary rocks E.g., Sandstone Primary minerals: Quartz and Feldspar Secondary mineral from weathering: Clay and Oxides Lithified (Compacted and cemented together) From Sand deposited by a river or beach

Minerals in Rocks Biochemical and bioclastic sedimentary Shells, Coral, Calcite and Dolomite in Limestone Lithified lime mud and Shell fragments Crystalline or Bioclastic Shells, Coral, Calcite and Dolomite in Limestone Lithified lime mud and Shell fragments Crystalline or Bioclastic

Minerals in Rocks Clastic sedimentary rocks E.g., Shale Primary mineral: Clay Minor mineral Quartz and Feldspar and Oxides From mud deposited in a deep lake, sea or ocean

Minerals in Rocks Metamorphic E.g. Schist Mica, Quartz and Feldspars Interlocking crystals (i.e., crystalline) Shale metamorphosed Minerals Changed in the solid state by heat and pressure

Minerals in Rocks Intrusive igneous rocks E.g., granite Quartz, Feldspar and a few Ferromagnesian minerals Tightly interlocking crystals (crystalline) Minerals formed from crystallizing magma

IV. Igneous Rocks A. Igneous Rocks and the Rock Cycle B. Basaltic Volcanism and Volcanic Rocks (extrusive igneous rocks) C. Silicic Volcanism and Volcanic Rocks D. Intrusive Igneous Rocks and E. Igneous Rock Classification A. Igneous Rocks and the Rock Cycle B. Basaltic Volcanism and Volcanic Rocks (extrusive igneous rocks) C. Silicic Volcanism and Volcanic Rocks D. Intrusive Igneous Rocks and E. Igneous Rock Classification

A.Igneous Rocks and The Rock Cycle Igneous Rock Solidification Magma Partial Melting Mantle Rock Fig 3.1 Geological Materials Transformation Processes See Kehew, Fig 2.53

Fig. 2.9 From bottom to top Increasing Fe/Mg/Ca Decreasing silica Increasing density Darker minerals 29% 14% <20% 20% <3% 23% <2% 25% (0) 33% (0) 23% (0) 15%* % of Tot. # of atoms Fe/Mg: Silicon: Quartz K and Na Feldspar Ca Feldspar Melting Points of Silicate Minerals Increasing Melting Temperature Olivine Pyroxene Group Amphibole Group Mica Group <700 o C > 1,100 o C

Melting of Granite (Quartz, Na Plagioclase, Biotite) Silicic Melt ~600 o C ~700 o ~800 o Quartz Melts Na-Feldspar First Begins to melt ~900 o ~1000 o Biotite begins Magma is enriched Magma is separated from solid to melt in Si, Na, Al (K) and melts upward in crust

Partial Melting and Magma E.g., Silicic mineral melt first Resulting in Silicic Magma Enriched: O, Si, Al, Na, K, Depleted: Ca, Fe, Mg Gasseous: (H 2 O, CO2) Poor in: O, Si, Al, Na, K, (<50%) Magma  Partial Melting Rich in: Ca, Fe, Mg (>50% wght) Fig 3.13

Solidification of Melts Magma, Intruded or Extruded, Solidifies (crystallizes) to form Intrusive or Extrusive Igneous Rocks Fig 3.12, 3.13 See Kehew, Fig 4.48

Igneous Rock E.g., Granite (Silicic, Intrusive Igneous Rock): Crystallized (Solidified) Silicic Melt Poor in: Fe, Mg, Ca, (<20%) Rich in: Silica (>70%) Quartz Na Plagioclase Biotite

Formation of Magma How are rocks melted? 1. Heating ■ 2. Depressurization 3. Increase water content 4. Increased silica content Where do rocks melt? Subduction zones (Silicic and Intermediate magma) Divergent Plate Boundaries Mantle Plumes (“Hot Spots”) Mafic Magma See Fig. 4.1 Hot and High Pressure Hot and High Pressure Hot and Low Pressure Hot and Low Pressure

Intrusive vs. Extrusive Silicic Magmas (& Lavas) Cool (<700 o C) Viscous Gaseous (steam of H 2 O and C0 2 ) Silicic Rocks Usually intrusive, course-grained, Silicic (Granite) to Intermediate (Diorite) rock forms plutons If extrusive, fine-grained rocks are formed by explosive volcanoes Rhyolite or Andesite Volcanoes  Also injects surrounding rocks with silica laden steam Batholith made of Plutons Fig 4.17 Composite Volcano

Dikes: Intruded near a pluton Silica rich fluids and rare elements are injected into cracks in all directions Discordant: cutting across layers Forming deposits of Precious minerals Ores Precious metals

Extrusive vs. Intrusive Mafic Magmas (& Lavas) Hot (>1000 o C) Non-Viscous (runny, flows easily) “Dry” (no H 2 O or C0 2 ) Mafic Rocks Usually Extrusive, Fine-grained, Mafic (Basalt) rock forms oceanic crust, Shield Volcanoes and Basalt Floods If Intrusive, course-grained mafic rocks are formed Gabbro. If intrusive, Dikes and Sills more common. (Plutons don’t form) Fig 3.10

Mafic Sill: Intruded between layers Mafic magma is less viscous and hotter so Does not form plutons but Cuts along layers (Sills) or even across layers (Dikes) Also Baked Zones of adjacent country rock and Chill Zones within the intrusion

B. Basaltic Volcanism 1. Types of Rocks are controlled by  Fig. 3.7  2. Characteristics of volcanism which are contr. by  3. Types of eruptions which are controlled by  4. Type of lava which is contr. by  5. Source of lava which is contr. by  6. Plate tectonics  Fig. 3.22

Basalt Figs. 4.9, 4.11, 4.17, 4.18 ‘A’a Pahoehoe Vesicular Basalt Pillow Basalt Columnar Jointing Obsidian (Glass) 1.Types of Rocks Composition and Texture

2. Characteristics of Volcanism Fissures Fig Shield volcanoes Fig Cinder cones Fig Fissures Through Crust Fig. 4.1 Hawaii Cinder Cone Calderas atop of Kilauea Shield

3. Types of Eruptions Non-explosive Lava flows, streams, ponds, floods Fountains Spatter cones Pyroclastic eruptions

5. Source of Lava 4. Types of Lava Types of lava Basaltic Hot Non-viscous Dry Partial melting of mantle Directly from mantle Mantle plumes Divergent plate boundaries

C. Silicic Volcanism 1. Types of Rocks  Fig. 3.7  2. Characteristics of volcanism  3. Types of eruptions  4. Type of lava  5. Source of lava  6. Plate tectonics  Fig Fig. 3.7 Fig. 3.24

1.Types of Rocks Composition and Texture Andesite (and Rhyolite) Pumice (quenched glass froth) Porphyritic Texture (partial crystallization and extrusion) Welded Tuffs (welded pyroclastics) Breccias (welded, coarse, angular pyroclatics) Fig mm Fig. 4.10

2. Characteristics of Volcanism Lava Domes Composite Volcanoes Layers of Pyroclastics (or tephra), ash and Lava flows Fig Fig Pyroclastic Layers

3. Types of Eruptions Mt. St. Helen’s Cascade Range Explosive Pyroclastic Flows and surges Lahars (saturated pyroclastics) Fig. 4.1 Fig Box. 4.19

1 mile Mt. St. Helen’s Before and After

4. Types of Lava Silicic Cool Viscous Gaseous

5. Source of Lava Partial melting at Subduction Zone Partial melting of continental crust Convergent plate boundaries Fig. 3.24

Igneous Rock Classification Intrusive (Plutonic) Extrusive (Volcanic) E.g., Basalt and Gabbro have two minerals Pyroxene Ca-Feldspar Kehew Figure 4.58 Lab Manual Fig. 3.8 Volume Percent of Minerals Continental Crust Oceanic Mantle Crust

Igneous Rocks and Silicates The Igneous Rock Classification parallels the systematic Silicate Mineral Classification Volume Percent of Minerals Frame- Double Single Iso. work Sheet Chain Chain Fig. 2.9

Igneous Rock Classification Intrusive Extrusive Silicic Intermediate Mafic Granite Diorite Gabbro Rhyolite Andesite Basalt Fig. 3.7 (Porphyritic)

1200 o C 1000 o Bowen’s Reaction Series Two series of minerals formed during crystallization of magma Intrus. Extrus. Gabbro Basalt Diorite Andesite Granite Rhyolite Intrus. Extrus. Gabbro Basalt Diorite Andesite Granite Rhyolite Low Silica Magma High Silica Magma Frame- Double Single Isolated work Sheet Chain Chain Temperature of Crystallization 750 o Kehew, Figure 4.53 (upside down)

Crystallization of Gabbro and Basalt If melt is extracted Ultramafic Rock will be formed Mafic Melt ~1,450 o C ~1,400 o ~1,350 o The remaining melt is enriched in silica (Int-Felsic) Ca-Feldspar Olivine Olivine converts Forms Forms to Pyroxene ~1,300 o ~1,250 o Gabbro Basalt Remaining silica crystallizes into Ca-Feldspar. Intrusive Extrusive Cooling: Slowly Quickly

Crystallization of Diorite and Andesite If cooled slowly in the magma chamber then extruded, Andesite Porphyry will be formed Intermediate Melt ~1,400 o C ~1,300 o ~1,200 o Ca Feldspar Olivine converts Ca Feldspar Forms to Pyroxene absorbs Na ~1,100 o ~1,000 o Diorite Andesite Pyroxene converts Remaining silica Intrusive Extrusive to Amphibole forms Na-Ca Fldspr. Slowly Cooled Quickly Cooled

Crystallization of Granite and Rhyolite Silicic Melt ~1,200 o C ~1,100 o ~1,000 o Na-Feldspar Pyroxene Pyroxene dissolves forms and grows forms to form Amphibole ~900 o ~750 o Granite Rhyolite Amph. dissolves Remaining silica Intrusive Extrusive to form Biotite forms Quartz Slowly Cooled Quickly Cooled

Dark Blue (to black) lines are Oceanic Trenches Light blue long light blue regions within the darker blue ocean basins are Mid-Ocean Ridges Red linear regions on continents are mountain ranges Reading the features Physiographic Map of the World

Vocanic Hazards Volcanic Earthquakes Directed Blast Tephra Volcanic Gases Lava Flows Pyroclastic Flows and Surges Lahars Debris Avalanches, Landslides, and Tsunamis

Hawaii Hazards