Rock Formation and Types: Igneous and Sedimentary Rocks

1. ROCKS Chapter 6

2. What is a Rock? • A group of minerals bound together • Can be mostly one mineral or several different minerals • Classified according to how they are formed. • 3 types

3. Rock Formation • Igneous: cooling and hardening of hot, molten rock, or magma, from inside the Earth.

4. Rock Formation • Sedimentary: compacting and cementing of layers of sediment. • Sediments – rock fragments, plant & animal remains, minerals that settle onto lake and ocean bottoms

5. Rock Formation • Metamorphic: formed by the effect of heat and pressure on other rocks

6. The Rock Cycle

7. Chapter 6.2 – Igneous Rocks

8. Igneous Rocks • Classified according to their mineral composition and texture • Made up of volcanic ash or magma • Texture depends on the cooling rate

9. Types of Magma • Felsic • Thick and slow-moving • Mostly Silica with some calcium, iron, and magnesium • Forms light-colored rocks - ex: quartz and orthoclase feldspar

10. 2. Mafic • Hotter, thinner and more fluid • Mostly iron and magnesium with some silica • Usually have large amounts of dark silicate minerals such as hornblende, augite, and biotite.

11. Rate of Magma Cooling Depends on where the magma cooling occurs Underground: • Magma cools very slowly (thousands of years) • Called Intrusive Rock • Course-grained texture • has time to form large crystals

12. At the Surface: • Volcanic eruptions release lava • Cools and hardens very quickly • Called Extrusive Rock • Fine-grained texture • Does not have time to form large crystals = glassy

13. Sometime underground magma begins to cool and is then suddenly forced to the surface • Creates a rock with large crystals surrounded by tiny crystals called porphyry

14. Igneous Rock Families • Grouped according to mineral composition. May include intrusive and extrusive rocks. • Granite Family • Gabbro Family • Diorite Family

15. Granite Family • Form from Felsic Magmas • Usually Coarse-grained • Typically contain quartz, feldspar, mica, and hornblende minerals Members: Granite, Obsidian, Pumice, Felsite, Rhyolite

16. Granite Rocks • Intrusive • Coarse-grained • Color: ranges from white or gray to pink • Commonly found in Mountainous areas

17. Gabbro Family • Mafic rock • Dark in color and denser than Granite

18. Diorite Family • Intermediate composition – neither felsic or mafic • Color: medium grays and green (darker than granites and lighter than gabbros)

19. Igneous Intrusions

20. Igneous Intrusions • Volcanoes give only a hint of the amount and the activity of the magma that exists below Earth’s surface • Forces deep with Earth may push magma into fractures in the bedrock. • Magma may be squeezed between rock layers, forcing the overlaying rocks upward to for domes • Great masses of magma may solidify far below the surface to form the cores of mountains

21. Pluton • Any igneous intrusion • A rock mass that forms when magma cools inside Earth’s interior • Pluton reaches Earth surface only after uplift and/or weathering take place.

22. Dikes • A sheet of igneous rock that cuts across rock layers vertically or at a steep angle • Formed when magma intrudes into angled cracks • May be hundreds of kilometers long and range from about a centimeter to many meters thick • Common in regions of volcanic activity

23. Sills • Sheet of igneous rock that lies parallel to the layers it intrudes • Formed when magma is forced between, not across, rock layers • Can be hundreds of meters thick and many kilometers long

24. Laccoliths • Magma that is stiff and does not flow easily • Forms a domed mass • The rock layers above laccoliths are also pushed upward to form a dome

25. Batholiths • Largest of all plutons • Forms the cores of many of Earth’s mountain ranges • Usually made of granite or granodiorite and can be thousands of square kilometers • Is exposed through uplift and erosion of overlaying rock layers

26. Chapter 6.3 – Sedimentary Rocks

27. Sedimentary Rocks • Form through the compacting and cementing of layers of sediment. • 3 Types of Sedimentary Rocks • Clastic Rocks • Chemical Rocks • Organic Rocks

28. Clastic Rocks • Formed from fragments of other rocks • Fragments come from the weathering of igneous, metamorphic, and other sedimentary rocks • Fragments rage from the size of pebbles to microscopic flakes

29. Clastic Rock Formation • Many fragments are moved by running water • Movement causes fragments to become smooth

30. Fragments are deposited in lakes or oceans • Larger fragments fall out and settle first then smaller particles • Over time settled fragments become cemented with silica, calcite, iron oxide or clay mineral. • Pressure can also cause sediments to stick together

31. Summarize in your own words the formation of clastic rock.

32. Clastic Rock Examples 1. Conglomerate • Large fragments ranging from gravel to boulders • Any mineral composition • Porosity and permeability depend on the degree of cementation

33. 2. Sandstone • Small particles – about the size of the head of a pin • Commonly quartz grains • Often highly porous and permeable

34. 3.Shale • Sediments very small about the size of flour particles • Clay minerals • Not very porous or permeable

35. Chemical Rock Formed from the accumulation of dissolved minerals in water Examples: Halite and Rock gypsum

36. Organic Rock • Formed from sediment remains of plants and animals Example: Limestone

37. Compare and contrast chemical and organic rock.

38. Features of Sedimentary Rocks • Stratification: visible layers • Formed when different types of sediments are laid down

39. Fossils: the remains, impressions, or any other evidence of a plant or animal preserved in rock. • Sediment covers the animal/plant filling in all of the pores which gradually turn into stone.

40. Ripple Marks: sand patters formed by wind, streams or waves that harden into stone.

41. Mud Cracks: form when deposits of wet clay dry and contract. Cracks become filled with different sediments and fossilize.

42. Nodules, Concretions, and Geodes • Nodules: lumps of fine-grained silica within limestone • Concretions: round, solid masses of calcium carbonate within shale • Geodes: spheres of silica rock within limestone

43. Describe three features of sedimentary rocks. Which feature is common to nearly every type of sedimentary rock?

44. METAMORPHIC ROCKS

45. Metamorphic Rock Metamorphism: process by which a rock’s structure is changed by pressure, heat, and moisture. • Are formed from preexisting rocks called parent rocks • May cause a change in chemical composition, texture, or internal structure • Pressure may force grains closer together, making the rock more dense and less porous.

46. Draw a picture of a conglomerate rock • Draw a second picture of how you think that rock will look once it has undergone metamorphic pressure

47. 2 Types of Metamorphism • Regional • Local

48. Regional Metamorphism • Large areas of rock change form after exposure to intense heat and pressure • As mountains form, deeply buried rocks are subjected to high heat and pressure

49. Local Metamorphism 2 Types • Contact Metamorphism: hot magma moves into the rock, heating and changing it

50. 2. Deformational Metamorphism: • Occurs at lower temperatures and at high pressure caused by stress and friction • Often along fault lines • As the masses move, heat and pressure cause the rock to deform (change shape).