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Chapter 3 Rocks. Rock – any solid mass of mineral or mineral-like matter that occurs naturally as part of our planet –Usually solid mixtures of minerals.

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Presentation on theme: "Chapter 3 Rocks. Rock – any solid mass of mineral or mineral-like matter that occurs naturally as part of our planet –Usually solid mixtures of minerals."— Presentation transcript:

1 Chapter 3 Rocks

2 Rock – any solid mass of mineral or mineral-like matter that occurs naturally as part of our planet –Usually solid mixtures of minerals –Some composed of just one mineral –Each mineral retains its properties in mixture

3 The Rock Cycle Three Major Types –Igneous –Sedimentary –Metamorphic Interactions among three things cause rocks to change from one type to another: –Water –Air –Land Rock cycle – continuous processes of rocks changing

4 The Rock Cycle – Igneous Rocks Magma – molten material that forms beneath Earth’s surface Lava – magma that reaches the surface Igneous rocks –Form when magma cools and hardens beneath surface -OR- –Volcanic eruption

5 The Rock Cycle – Sedimentary Rocks Weathering – rocks are physically and chemically broken down by water, air, living things. Sediments – weathered pieces of earth materials –Moved by water, gravity, glaciers, wind Sedimentary rocks formed by: –Sediments being compacted and cemented

6 The Rock Cycle – Metamorphic Rock Sedimentary rock – buried deep within Earth –Exposed to increased pressure and temp Metamorphic rock formed: –Sedimentary rock exposed to extreme pressure and temp When metamorphic rocks exposed to additional pressure or higher temps: –Melt to form magma -> eventually crystallizes to form igneous rock again

7 Alternate Paths Igneous Rock: –Some remains deeply buried: exposed to strong forces & increased temp – becomes metamorphic rock –If pressure & temp high enough – could melt and reform igneous Metamorphic and sedimentary: –Could weather to become sediments again –Then become sedimentary rocks again

8 Energy Igneous & metamorphic rocks –Both driven by heat from Earth’s interior Sedimentary rocks –Weathering and movement of weathered materials –External processes powered by energy from the sun

9 Dynamic Rock Cycle

10 Igneous Rocks Different kinds of igneous rock form when magma and lava cool and harden –Intrusive –Extrusive

11 Intrusive Igneous Rocks Form when magma hardens beneath Earth’s surface –Intrude into existing rocks –Common rock: granite

12 Extrusive Igneous Rocks Form when lava hardens –They are extruded onto the surface –Common: rhyolite

13 Classification of Igneous Rocks Two main characteristics: –Texture Size Shape Interlocking crystals –Composition light vs. dark minerals

14 Igneous Rocks – Texture 1.Coarse-grained –Slow cooling results in formation of large crystals 2.Fine-grained –Rapid cooling results in small, interconnected mineral grains

15 Igneous Rocks – Texture 3.Glassy –Formed when ions in lava do not have enough time to arrange themselves in network of crystals –Ex. – obsidian, pumice 4.Porphyritic – (large crystals surrounded by fine-grained minerals) –Formed when minerals that crystallize from magma do not form at same rate or same time

16 Igneous Rocks – Composition 1.Granitic Composition Light-colored silicate minerals Major rocks of continental crust – 70% silica Ex – rhyolite: extrusive granitic rock 2.Basaltic Composition Dark silicate minerals & plagioclase feldspar Rich in iron and magnesium Darker and denser than granitic rocks Ex – basalt, gabbro

17 Igneous Rocks - Composition 3.Other Compositional Groups Andesitic composition – between granitic and basaltic rocks common volcanic rock – andesite 25% dark silicate minerals Peridotite – much of upper mantle Ultramafic – composed mostly of dark minerals Rare at Earth’s surface

18 Sedimentary Rocks Form when existing rocks broken down into sediments 1.Weathering - any process that breaks rocks into sediment 2.Erosion – water, wind, ice, gravity 3.Deposition – loses energy, drops sediment Sediments deposited according to size Largest deposited first – smallest deposited last

19 Sedimentary Rocks Processes that change sediments into sedimentary rocks: 1.Compaction – squeezes, or compacts sediments Much of the water is driven out 2.Cementation – dissolved minerals deposited in tiny spaces among sediments

20 Classification of Sedimentary Rocks Classified into two groups according to the way they form: 1.Clastic sedimentary rocks –rocks made of weathered bits of rocks and minerals –Conglomerate – gravel-sized or larger particles make up most of rock –Breccia – angular particles –Sandstone – sand-size grains

21 Classification of Sedimentary Rocks 2.Chemical and biochemical sedimentary rocks –Dissolved minerals precipitate from water solutions –Occurs when water evaporates or boils off, leaving a solid product –Limestones, rock salt, chert, flint, rock gypsum 90 % of limestones formed from biochemical sediments Shells and skeletal remains of organisms on ocean floor

22 Features – Sedimentary Rocks Can give clues to how, when, and where rocks formed 1.Each layer: records a period of sediment deposition Oldest layers found at bottom 2.Ripple marks: rock formed along beach or stream bed 3.Mud cracks: record of a dry environment 4.Fossils: answer questions about rocks –Did rock form on land or ocean? –Was climate hot or cold? –Match rocks from different places (compare age)

23 Metamorphic Rocks Existing rocks are changed by heat and pressure –Conditions are a few km below surface and extend into the upper mantle

24 Two Types of Metamorphism 1.Contact metamorphism: hot magma moves into rock Low-grade metamorphism Marble – forms from limestone

25 Two Types of Metamorphism 2.Regional Metamorphism During mountain building, large areas of rock subjected to extreme pressures and temps High-grade metamorphism

26 Agents of Metamorphism 1.Heat – most important agent Comes from two sources: magma and change in temp with depth Provides energy to drive chemical reactions Minerals are stable at different temps 2.Pressure (Stress) Increases with depth Pressure on rocks from within Earth comes from all directions Causes rocks to flow, not fracture Minerals flatten and elongate

27 Agents of Metamorphism 3.Hydrothermal Solutions When solutions increase in temp, reactions among substances occur at a faster rate Promote recrystallization by dissolving original minerals and depositing new ones

28 Classification of Metamorphic Rocks 1.Foliated Some minerals recrystallize at right angles to the direction of force Gives rock a layered or banded appearance Ex: shale – slate – schist – gneiss

29 Foliated Metamorphic ShaleSlate SchistGneiss

30 Classification of Metamorphic Rocks 2.Nonfoliated: Does not have banded texture Most only contain one mineral Limestone (made of calcite) - marble limestone marble


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