The Rock and Minerals of the Earth’s Crust

1. The Rock and Minerals of the Earth’s Crust

3. Minerals • A mineral is material formed when two or more elements combine in a crystalline structure • The 92 elements found in the Earth’s crust form at least 2000 different minerals

4. Common Minerals: Building Blocks of the Earth’s CrustSee page 68

5. Rocks • A rock is any consolidated mixture of one or more minerals • Oxygen and Silicon combine to form the silica tetrahedron (SiO4), the basic building block of the Earth’s crust. • The variety of rocks is only limited by the various combinations of minerals that occur in the Earth

6. Rocks • The composition of crustal rocks gives us a good idea of the composition of the crust and the interior of the earth. • Some rocks are very old- up to 3 billion years old, but more rocks are very young (well for rocks) Why do you think that most rocks are so young??

7. Answer • Due to the convection currents beneath the Earth’s surface put pressure on the crust, which causes the rocks of the ocean floor to move. In other portions of the crust disappear into the mantle at deep trenches on the ocean floor. Therefore, the constant recycling of rocks results in rocks no older than 2-3 million years old. However the rocks of the continents are much older

8. Answer • Second part lies in the hydrosphere. • The movement of water and ice play a major role in eroding older rocks and the deposition helps account for the youthful age of many rocks of the Earth’s crust

9. The Rock Cycle • The process of replacing of older rocks with new ones is referred to as the Rock Cycle

10. Rock Cycle Con’t • There are 3 rock classes: • igneous (cooling/solidification) • sedimentary (erosion/deposit) • metamorphic(heat/pressure)

13. Activity • Using the chart 5.3 (pg 69) in your textbook create your own rock cycle. • Ensure that factors contributing to their formation are present (ex. Heat/pressure) • Ensure it is titled • Ensure it has colored corresponding arrows • Ensure it has your name on it **When you are done complete questions 1,3, and 4 on page 70 **

14. Born of Fire: Igneous Rocks

15. Igneous Rocks • 95% of the rocks on the Earth’s crust • Formed by the cooling and solidification of molten materials, or magma beneath the Earth’s surface • The term igneouscomes form the Latin word fire • Which refers to the origin of these rock- VOLCANIC ERUPTIONS

16. Major Igneous Rocks • There are two main categories of Igneous Rocks: • 1. Extrusive (Volcanic): cool on the surface • 2. Intrusive(Plutonic): Cool below the Earth’s surface

17. Extrusive Rocks • Rapid cooling occurs when molten magma is erupted onto the Earth’s surface and is exposed to the Atmosphere. • Magma that reaches the Earth’s surface is called Lava • Heat is given off quickly and lava solidifies into hard rock (or smooth volcanic glass) • Sometimes the rocks cool so quickly that gas does not have time to escape (ex. Pumice)

19. Intrusive Igneous Rocks • Where mama cools slowly below the Earth’s surface. • These rocks are much different in appearance • Slow cooling allows the various elements to gather together to form crystals of pure minerals that are visible with the eye. • Granite is the most common rock of this category.

20. Examples of Igneous Rock

21. Born of Erosion and Deposition: Sedimentary Rocks • The energy for the creation of sedimentary rock comes largely from the sun rather than the Earth’s interior • Closely related to the movements of water (hydrological cycle) • Formed from sediments • Many areas only have layers of sedimentary rocks that are skin deep.

22. Born of Erosion and Deposition: Sedimentary Rocks • These sediments have many origins and sizes; however, they can be divided into two types: • Clastic (inorganic): gravel, sand, silt, etc. • Non-Clastic (organic): solids from ocean waters are made up of animal or plan remains

23. Clastic Sedimentary Rocks • Settle out of relatively calm waters, the build up horizontal layers of the floors of these lakes or oceans • These sediments turn to rock by two main processes: • 1. pressure from more recent overlying sediments • 2. lithification: cementing together the sediments by various chemicals (ex. Calcium carbonate) that seep into the layers.

24. Clastic Sedimentary Rocks • Today these types of rocks are slowly forming in many parts of the world. However, they are most productive in forming areas where major river deposits sediments into the ocean, forming huge deltas.

25. Non-Clastic Sedimentary Rocks • Originate from the remains of plans and animals (usually skeletons or shells) that accummulate on the ocean and sea floors, or from the chemical precipitation of minerals from seawater. • These take longer to form than Clastic Sedimentary Rocks, but make up common rocks such as: • Limestone • Dolomite • Shale, • Sandstone • Coal

26. Non-Clastic Sedimentary Rocks • The Great Barrier Reef of Australia and the reefs of the Caribbean Sea and Pacific Ocean are areas where limestone rocks are presently being formed fromt eh remains of sea creatures and coral reef.

28. Origins of Important Sedimentary Rocks

29. Examples of Sedimentary Rocks

30. Born of Great Heat and Pressure: Metamorphic Rocks • Name comes from the word “metamorphosis” meaning change. • Rocks that have been greatly altered from their original forms through hit and pressure fit into this category

31. Metamorphic Rocks • We cannot observe metamorphic rocks forming, as with igneous and sedimentary rocks. • Often the heat and pressure that transform these rocks are found deep with Earth’s surface where mountain ranges are forming. • Form where crustal plates collide pushing up new mountain ranges such as the Himalayas, Andes, Rockies, and Alps

32. Metamorphic Rocks • The term foliatedis used to describe the structure caused by gathering together of different minerals into parallel bands. Do not confuse this with the layers of sedimentary rocks • Common Characteristics: • Hard to break (very compact) • Reflection of their origins in their roots of the mountains

33. Uses of Metamorphic Rocks • Slate and marble are rocks useful for building purposes, as they are very durable • Seldom contain old, natural gas, or coal because the materials would be burnt up due to the immense heat and pressure put on these rocks • Metal are found in these rocks due to the minerals that igneous rocks possess before being exposed to the elements

34. Examples of Metamorphic Rocks

35. Oceans and Continents • The division of the Earth’s materials into the three major rock classes is only one way to consider them. • A second way to classify rocks is by dividing them into two categories: 1. those found in the ocean, and 2. those found on continents. • These tow groups of rocks have different densities and generally different colors

36. Oceans and Continents • The term sialis used to identify the granitic rocks of the continents since they are primarily comprised of silicon and aluminum. • These rocks are less dense than basaltic rocks that lie in the ocean as they are comprised of lighter elements.

37. Oceans and Continents • On the other hand, the term simais used for denser basaltic rocks of the ocean floor, as they are primarily comprised of silicon and magnesium. • Iron is present in greater amounts in these rocks. • Usually darker in color than the granitic continental rocks

38. Theory of Isostacy: Balance Between Crust and Mantle • Isostacy: state of balance maintained by the earths crust as it floats on the plastic layer of the upper mantle • The difference in density between the granitic and basaltic rocks is the key to development of continents and ocean basins. • It is believed that the various blocks of the crust float on the softer materials of the asthenosphere