Rocks and Rock Cycle Intro.

Rocks are not what they seem. They are constantly changing. The Rock Cycle or happen very quickly. Changes can take millions of years

Sedimentary Rock Igneous Rock eg granite eg basalt large crystals small crystals very high temperatures causing melting cooling and crystallisation (solidification) weathering and erosion fast cooling slow cooling very hot! mudstone Magma (molten rock) Sediment mud sand shells sediment is compacted (squashed) and particles get cemented Metamorphic Rock limestone eg chalk sandstone marble slate heat and pressure Any rock can be weathered or eroded to mud or sand

The Rock Cycle

Causes of Change Causes of rocks to change from one type to another. Causes of rocks to change from one type to another. Weathering Weathering Erosion Erosion Compaction Compaction Cementation Cementation Heat & Pressure Heat & Pressure Melting and cooling Melting and cooling

Causes of Change

Igneous Rocks Earth’s original!!

Igneous Types Intrusive (magma) Slow cooling Slow cooling Large crystals (course-grained) Large crystals (course-grained) Extrusive (Lava) Fast cooling Fast cooling Small Crystals (fine- grained) Small Crystals (fine- grained)

Magma Composition Composition Contains the same elements/compounds of earth’s crust Contains the same elements/compounds of earth’s crust Therefore silica & oxygen most abundant Therefore silica & oxygen most abundant Categorized by the amount of silica & oxygen content Categorized by the amount of silica & oxygen content

Igneous Classification

Magma Origins Minerals begin melting between o C Minerals begin melting between o C Factors that affect melting Factors that affect melting 1. Temperature Increases w/depth (geothermal gradient) Increases w/depth (geothermal gradient) 2. Pressure Increases w/depth Increases w/depth 3. Water content More water lower melting point More water lower melting point

How Rocks Melt Partial melt Partial melt Some minerals melt faster than others Some minerals melt faster than others Creates a magma slush Creates a magma slush Fractional crystallization Fractional crystallization Some minerals cool at lower temps Some minerals cool at lower temps Cools in reverse order of melt Cools in reverse order of melt

Crystal Settling

Bowen’s Reaction Series

Bowen’s Reaction Series Bowen’s Reaction Series Illustrates the relationship between cooling magma and mineral formation Illustrates the relationship between cooling magma and mineral formation 2 main branches 2 main branches Continuous Feldspar group Continuous Feldspar group Discontinuous iron-magnesium group Discontinuous iron-magnesium group

Bowen’s Reaction Series Bowen’s Reaction Series Continuous Feldspar Group As magma cools composition gradually changes As magma cools composition gradually changes Calcium-rich cools high temps. Calcium-rich cools high temps. Sodium-rich cools lowest temps. Sodium-rich cools lowest temps. This means the previously cooled minerals react with the magma to form new (different) minerals

Bowen’s Reaction Series Bowen’s Reaction Series Iron-rich minerals Minerals change suddenly at dif. Temps Minerals change suddenly at dif. Temps Olivine cools o C using up iron & magnesium Olivine cools o C using up iron & magnesium When too little Iron & magnesium is left for olivine formation, pyroxene will form When too little Iron & magnesium is left for olivine formation, pyroxene will form As more iron & magnesium get used the minerals that follow are more silica & oxygen rich As more iron & magnesium get used the minerals that follow are more silica & oxygen rich Therefore rocks abundant in silicate minerals form last (Quartz) Therefore rocks abundant in silicate minerals form last (Quartz)

Chemical Makeup Felsic (comes from Feldspar & Silica) Light color & low density Light color & low density Make up most of the continental crust. Make up most of the continental crust. Ex/ mica, quartz, feldspar Ex/ mica, quartz, feldspar

Chemical Make-Up Mafic (comes from Magnesium & Ferros/Iron) Dark colored and high in density Dark colored and high in density Main type of rocks in the oceanic crust. Main type of rocks in the oceanic crust. Ex/ Gabbro & Basalt Ex/ Gabbro & Basalt Ultramafic –very low silica and high iron & magnesium Extremely dark in color Extremely dark in color

Glassy Texture No crystal shapes and are either massive (obsidian) or frothy (pumice or scoria)

Coarse Texture Course textures have mineral crystals large enough to be clearly seen Slow cooling

Fine Grained Texture Fine grains and crystal are not able to be distinguished w/the naked eye Fast cooling

Porphyritic Textures Course-grained crystals surrounded by fine- grained Course-grained crystals surrounded by fine- grained Two cooling histories: slowly then quickly Two cooling histories: slowly then quickly