What might you expect to find if you examined a rock under a microscope?

1. Section Check What might you expect to find if you examined a rock under a microscope? A rock is a naturally formed mixture containing minerals, rock fragments, or volcanic glass. Underground igneous rocks form from molten rock material called _______. Magma Extrusive igneous rocks form when _______ cools. lava and ash

2. Sedimentary Rocks, Metamorphic Rocks, and The Rock Cycle Notes Chapter 26 Sections 3 & 4

3. Clasts • Rock is a consolidated mixture of minerals. Some of these minerals could be in bits and pieces of other rocks. Such small rock and mineral fragments are called clasts. • Rocks inside Earth are protected from surface conditions. • Rock on Earth’s surface are exposed to water, wind, and other forces.

4. Transportation and Deposition • Mechanical weathering processes break down rocks into smaller clasts. • When clasts are transported to new locations, they often become rounded before being deposited. • When clasts are loose on Earth’s surface, they don’t fit together perfectly. The empty space in between the grains is called porespace.

5. Compaction and Cementation • When buried by more sediment deposited above them, clasts can be smashed together with great force. • The process by which clasts stick together due to the weight of overlying material is called compaction.

6. Compaction and Cementation • Water moving between clasts carries dissolved minerals that can act as cement. • Minerals precipitate slowly out of a water solution and crystallize in the spaces between clasts in a process called cementation. • Most of the time both compaction and cementation work together to make sedimentary rock.

7. Detrital Sedimentary Rock • Detritusis another name given to clasts. • Sedimentary rocks that are made mostly of clasts are called detrital sedimentary rock. • In order of decreasing size, clasts are known as gravel, sand, silt, or clay.

8. Detrital Sedimentary Rock • Geologists classify detrital sedimentary rocks based on clast size. • The size of the clast can be used to infer how the clast was transported. • It takes more force, or energy, to lift or move gravel than it does to lift or move sand.

9. Composition • Detrital sedimentary rock composition depends on the types of weathered rock material that is transported, and eventually deposited.

10. Detrital Sedimentary Rock • Clast size also provides clues to help determine the depositional environment of the sediment that formed the detrital rock.

11. Chemical Sedimentary Rocks • Chemical sedimentary rocks form from water that contains dissolved solids. • If water receives more dissolved materials than it can hold in solution, then the excess solid precipitates as mineral crystals. • Mineral crystals also precipitate out of a solution through evaporation. • This leaves an oversupply of dissolved matter and again crystals.

12. Biochemical Sedimentary Rocks • If sedimentary rocks contain the remains of living organisms they are called biochemical sedimentary rocks. • Limestone is composed partly, of the remains of marine organisms that had hard parts made of calcium carbonate. • Coal is a biochemical sedimentary rock composed almost entirely of the carbon that remains after plant material is compressed underground.

13. Metamorphic Rocks • Metamorphic rocks, have been changed by a combination of heat, pressure, and chemical reactions. • Any igneous, sedimentary, or metamorphic rock can be changed by metamorphism.

14. Textures • Foliated rocks have crystals that are arranged in layers and bands. • Nonfoliated rocks have crystals with more random orientations.

15. Foliated Rocks • Slate is a fine-grained foliated metamorphic rock that splits easily along flat planes. • Slate forms when shale is compressed causing minerals, like mica, to oriente perpendicular to compression.

16. Nonfoliated Rocks • Nonfoliated metamorphic rocks tend to have random crystal orientation and uniform grain size and uniform color. • Mineral grains tend to grow as the grade of metamorphism increases.

17. Metamorphic Rock Classification • Mineral composition provides clues about the original rock type before metamorphism, and indicates to what degree a rock had been metamorphosed.

18. The Rock Cycle • The continual changing of rocks from one type to another is called the rockcycle.

19. Section Check Question 1 Which is NOT an agent of metamorphism? A. chemical reactions B. pressure C. heat D. wind

20. Section Check Answer The answer is D. Wind is responsible for erosion on some rocks but it does not help form them.

21. Section Check Question 2 Describe foliated metamorphic rocks.

22. Section Check Answer Foliated textures in metamorphic rocks exhibit layering or mineral banding.

23. Section Check Question 3 Is there a beginning and end to the rock cycle? Answer No, the rock cycle is a continual process in which rocks change from one form to another.

24. End of Day Homework: None