Handout 2 of 14. (Topic 1.2) The Cycle of Change

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Student: Date received: Handout 2 of 14 (Topic 1.2) The Cycle of Change The Bernese Alps (central Switzerland) as viewed from the southeast from the Earth Observatory (http://earthobservatory.nasa.

1 Student: Date received: Handout 2 of 14 (Topic 1.2) The Cycle of Change The Bernese Alps (central Switzerland) as viewed from the southeast from the Earth Observatory ( E-77377_lrg.jpg). The strata that make up the Alps comprise igneous, sedimentary and metamorphic rocks that are continuously uplifted, eroded and transported. In this area one of the main agents of erosion are glaciers. The mountain in the centre of the image is the Eiger.

2 The Cycle of Change Key Ideas Rocks are generally classified as igneous, sedimentary, or metamorphic. Rocks are in a constant process of change. Intended Student Learning Describe in general terms the formation of igneous, sedimentary, and metamorphic rocks. Relate specific temperature and pressure conditions that occur in different parts of the Earth s crust to mineral changes. Use a simple diagram to explain how processes and materials interact to make up the rock cycle. Topic 1.2 The Cycle of Change Page 2 of 10

3 1.2 THE CYCLE OF CHANGE CLASSIFICATION & FORMATION A rock is defined as any solid, naturally-occurring part of Earth's crust. The rocks of Earth's crust are divided into three groups: IGNEOUS METAMORPHIC SEDIMENTARY Igneous rocks are formed when hot molten rock (magma) cools and solidifies. e.g. Granite, basalt. Sedimentary rocks may be formed by many processes. The most common sedimentary rocks are formed by cementation of fragments weathered from older rocks. e.g. Sandstone, shale Many sedimentary rocks are formed from the remains of living organisms. e.g. Fossiliferous limestone, coal Metamorphic rocks are formed by the action of heat and pressure on existing rocks. e.g. Slate, marble PRESSURE, TEMPERATURE & MINERALS We know that the water pressure exerted on a submarine deep under the sea is very high due to the weight of water above the vessel. Similarly, the pressure on rocks deep within Earth's crust is also very high, due to the weight of overlying rocks. The diagram below is a graph of depth versus temperature. Geothermal gradient for continental crust Temperature ( C) Depth (km) Topic 1.2 The Cycle of Change Page 3 of 10

4 As indicated in the above diagram, direct observation in deep mines (to 3000 metres) or deep oil wells (to 9000 metres) indicate that the temperature of Earth's crust increases with depth. The rate of increase of temperature with depth is called the geothermal gradient. The average geothermal gradient is about 30 C per kilometre, but it varies from place to place. The geothermal gradient in the Cooper Basin of northeastern South Australia and south-western Queensland is an area where the geothermal gradient is particularly high. In this area, temperatures of rocks at depths of 4 to 5 km reach 300 C. Considerable government and private monies are being invested to develop these hot rock resources for the generation of electricity. This important topic will be considered more fully later in the course. The temperature and pressure conditions under which igneous, sedimentary and metamorphic changes occur are summarised in the diagram below. The common rock-forming minerals studied in the previous unit, are not all stable under the same conditions of temperature pressure. For example, clay minerals, which are found in many sedimentary rocks, are stable under the low temperature and conditions that occur near Earth's surface. If these minerals are subjected to very high temperatures and pressures, they change to other minerals especially the micas biotite and muscovite. Conversely, micas are formed under high temperature and pressure conditions and therefore usually found in igneous and metamorphic rocks. When igneous and metamorphic rocks are exposed at Earth's surface, their mica minerals gradually weather to form (surface stable) clays. In general: minerals that are stable at low temperatures and pressures conditions are found in sedimentary rocks. minerals that are stable at high temperatures and pressures are found in igneous and metamorphic rocks. Topic 1.2 The Cycle of Change Page 4 of 10

5 Quartz is stable under a very wide range of temperature and pressure conditions, and is therefore found in all rock types - igneous, sedimentary and metamorphic. The table below describes the conditions under which the common rock-forming minerals (listed in your syllabus) are stable and indicates the rock types in which they are usually found. Mineral Pressure & temperature conditions for stability Rock type that the mineral occurs in Quartz Wide range of conditions All types Feldspars High temps & pressures Igneous & metamorphic Biotite High temps & pressures Igneous & metamorphic Muscovite High temps & pressures Igneous & metamorphic Hornblende High temps & pressures Igneous & metamorphic Olivine Very high temperatures Igneous Calcite Clay minerals (e.g. kaolinite) Wide range of temps & pressures (recrystallises) Low temps & pressures Sedimentary & metamorphic Sedimentary THE ROCK CYCLE During the course of geological time (i.e. hundreds of millions of years), new mountain ranges are pushed up and old ones eroded away. Temperature and pressure conditions acting on rocks within Earth's crust gradually change. Consequently, new minerals (and therefore new rocks) are formed. Rocks are continually recycled. The diagram below shows the rock cycle. It illustrates the processes by which rocks gradually changes to others. Topic 1.2 The Cycle of Change Page 5 of 10

6 Topic 1.2 The Cycle of Change Page 6 of 10

7 CLASSIFICATION & FORMATION 1. What is a rock? EXERCISES 2. Name the three groups into which Earth's crustal rocks are classified. 3. Explain how the rocks in each group were formed. IGNEOUS: SEDIMENTARY: METAMORPHIC: Topic 1.2 The Cycle of Change Page 7 of 10

8 4. In the right hand side of the following table, write the numbers of the specimens that fit the corresponding descriptions in the left hand column. Note that more than one specimen may fit each description. DESCRIPTION OF SPECIMEN/S SPECIMEN NUMBER/S Black in colour Formed from living organisms Particles easily scraped off Very hard rock/s (scratch knife blade) Shows effect of great pressure Contains visible particles (grains) Grains invisible to the naked eye Effervesence with acid 5. You should now have enough information to enable you to try and identify the majority of your rock specimens. The table below gives their names and groups. Enter the appropriate specimen numbers. IGNEOUS ROCKS SEDIMENTARY ROCKS METAMORPHIC ROCKS NAME NUMBER NAME NUMBER NAME NUMBER Basalt Sandstone Marble Granite Shale Slate Pumice Fossil l/stone PRESSURE, TEMPERATURE & MINERALS Schist 1. How do we know that temperature increases with depth below Earth's surface? 2. What is the name given to the rate of increase of temperature with depth? Topic 1.2 The Cycle of Change Page 8 of 10

9 3. The diagram below shows the variation of temperature with depth below Earth's surface. The shaded areas represent regions where different types of rock-forming processes occur. Indicate on the diagram the type of rock-forming process that occurs in each of the shaded areas. 4. Use the above diagram to complete the following table, by stating which type of process occurs at each of the temperatures and depths indicated. TEMPERATURE ( C) DEPTH (km) TYPE OF PROCESS Explain why some minerals are found only in sedimentary rocks and others in igneous and metamorphic rocks. 6. Name one mineral which is found in all rock types, and explain why this is so. Topic 1.2 The Cycle of Change Page 9 of 10

10 THE ROCK CYCLE 1. Explain how rocks are continually being 'recycled'. 2. Fill in the spaces in the diagram below, which refer to the rock cycle. The processes by which rocks change from one type to another are: Heat and pressure, Weathering and erosion, Solidification of magma, Compaction and cementation, Melting. Each process may occur more than once. Topic 1.2 The Cycle of Change Page 10 of 10

Practice Test Rocks and Minerals. Name. Page 1

Name Practice Test Rocks and Minerals 1. Which rock would be the best source of the mineral garnet? A) basalt B) limestone C) schist D) slate 2. Which mineral is mined for its iron content? A) hematite