Rocks & The Rock Cycle

1. Rocks & The Rock Cycle Earth Science Fall 2013

2. Vocabulary • Batholith- intrusive formation with at least a surface exposure of 100 square kilometers and reaching a depth of thousands of meters

3. Vocabulary • Breccia- elastic sedimentary rock composed of angular fragments

4. Vocabulary • Cementation- process in which dissolved minerals left by water passing through sediments bind sediments together

5. Vocabulary • Chemical sedimentary rock- rock formed from minerals that precipitate out of water

6. Vocabulary • Clastic sedimentary rock- rock made up of fragments from pre-existing rocks

7. Vocabulary • Compaction- process in which air and water are squeezed out of sediments, resulting in the formation of sedimentary rock

8. Vocabulary • Concretion- nodule of rock with a different composition from that of the main rock body

9. Vocabulary • Conglomerate- sedimentary rock composed of rounded gravel or pebbles cemented together by minerals

10. Vocabulary • Contact metamorphism- change in the structure and mineral composition of rock surrounding an igneous intrusion

11. Vocabulary • Dike- igneous intrusion that cuts across rock layers

12. Vocabulary • Evaporites- sedimentary rocks formed from minerals left after water evaporates

13. Vocabulary • Extrusive igneous rock- rock formed from molten lava that hardens on the earth’s surface

14. Vocabulary • Foliated- describing metamorphic rock with parallel bands

15. Vocabulary • Fossil- trace or remains of a plant or an animal in sedimentary rock

16. Vocabulary • Igneous rocks- rock formed from cooled and hardened magma

17. Vocabulary • Intrusive igneous rock- rocks formed from the cooling of magma beneath the earth’s surface

18. Vocabulary • Laccolith- flat-bottomed intrusion that pushes overlying rock layers into an arc

19. Vocabulary • Lava Plateau- raised flat-topped area made of layers of hardened lava

20. Vocabulary • Metamorphic rock- rock formed from other rocks as a result of intense heat, pressure, and chemical processes

21. Vocabulary • Metamorphism- changing of one type of rock to another by heat, pressure, and chemical processes

22. Vocabulary • Nonfoliated- describing a metamorphic rock without parallel bands

23. Vocabulary • Organic sedimentary rock- rock formed from the remains of organisms

24. Vocabulary • Porphyritic- describing an igneous rock composed of both large and small crystals

25. Vocabulary • Regional metamorphism- metamorphism that affects rocks over large areas during period of tectonic activity

26. Vocabulary • Rock cycle- series of processes in which rock changes from one type to another

27. Vocabulary • Sediment- fragments that result from the breaking of rocks, minerals, and organic matter

28. Vocabulary • Sedimentary rock- rock formed from hardened deposits of sediment

29. Vocabulary • Sill- sheet of hardened magma that forms between and parallel to layers of rock

30. Vocabulary • Stock- igneous intrusion with an area less than 100 square kilometers

31. Vocabulary • Stratification- layering of sedimentary rock

32. Vocabulary • Volcanic neck- solidified central vent of a volcano

33. Rocks & the Rock Cycle • Magma from the earth’s interior is the parent material for all rocks • From the time magma cools & hardens at or near the surface of the earth, the resulting rock begins to change. • Geologists have classified rocks into 3 major types based on the way the rocks are formed.

34. Rocks & the Rock Cycle • 3 major rock types • Igneous rock • Sedimentary rock • Metamorphic rock

35. Rocks & the Rock Cycle

36. Igneous Rocks • 2 groups of igneous rocksthat are classified according to where molten rock cools and hardens • Intrusive igneous rocks • Magma cools below the crust • Extrusive igneous rocks • Rapid cooling of lava on the earths surface

37. Igneous Rocks • Extrusive & intrusive igneous rocks differ mainly in their sized of crystalline grain and is known as texture • Texture is determine by the cooling rate of the magma or lava that formed the rock

38. Texture of Igneous Rocks • Slow loss of heat allows minerals to form large, well-developed crystalline grains • Coarse-grained texture • Ex: granite • Rapid loss of heat does not allow time for large crystalline grains to form, this produces fine-grained rock • Ex: basalt • Oceanic crust is made mostly of basalt

39. Texture of Igneous Rocks • Lava or magma cools slowly at first & then rapidly as it near the earth’s surface, relatively large crystals embedded within a mass of smaller ones • Porphyritic • Highly viscous, silica-rich magma cools rapidly and no crystals form • Ex: obsidian

40. Texture of Igneous Rocks • Magma that contains large amounts of dissolved gases hardens, the gases become trapped in the rock and produces rock full of holes • Ex: pumice

41. Mineral Composition of Igneous Rocks • Determined by the chemical composition of the magma from which the rock develops • Divided into 3 families • Felsic • Intermediate • Mafic

42. Mineral Composition of Igneous Rocks • Felsic rocks • Formed from magmas that are high in silica • Have light coloring of their main mineral components, orthoclase feldspar & quartz • May also contain plagioclase feldspar, biotite mica, & muscovite mica • Ex: granite , rhyolite, obsidian • Obsidian may be black, blue, or red depending on its chemical composition

43. Composition of Igneous Rocks • Mafic rocks • Form from magmas that are low in silica but rich in iron and magnesium • Also can include ferromagnesian minerals making them dark in color • Ex: basalt , gabbro

44. Composition of Igneous Rocks • Intermediate Rocks • Medium colored • Contain minerals such as plagioclase feldspar, hornblende, pyroxene minerals, biotite mica • Contain less quartz than the felsic family • Ex: diorite , andesite

45. Igneous Rock Structures • Intrusions • Largest of all intrusions are batholiths • Form cores of several major mountain ranges like the Sierra Nevada range in CA & the Coast Range in BC • A stock is similar to a batholith only much smaller • Laccoliths form when magma flows between rock layers and spread upward sometimes pushing the overlying rock into an arc • Frequently found in groups • Ex: Black Hills

46. Igneous Rock Structures • Sills form when a sheet of magma flows between layers of rock and hardens, it does not cause the arcing like a laccolith • Lie parallel to rock layers & vary in thickness from a few cm to hundreds of meters • Ex: Big Bend National Park in Texas • When magma forces its way through rock layers by following existing vertical fractures or by creating new ones and solidifies is called a dike • Common in areas of volcanic activity

47. Igneous Rock Structures • Extrusions • A volcano is a cone of extrusive rock surrounding a central vent, when a volcano stops erupting for a long period the cone gradually wears away and the solidified central vent is left, this is called a volcanic neck • A lava plateau develops from lava that flows out of long cracks in the earth’s surface

48. Sedimentary Rocks • Sedimentary rock is made up of accumulations of various types of sediments • Compaction & cementation are 2 processes that form sedimentary rocks • Sedimentary rocks are classified according to the kind & size of sediments that form them

49. Formation of Sedimentary Rocks • Clastic sedimentary rock is made up of rock fragments carried away from their source by water, wind, or ice & left as deposits elsewhere • Chemical sedimentary rock forms from minerals that precipitate from water • Organic sedimentary rock forms from the remains of organisms

50. Clastic Sedimentary Rocks • Classified by the size of the sediments they contain • Conglomerate- rock composed of rounded gravel sized fragments or pebbles • Breccia- rock made of rock fragments that are angular & have sharp corners • In both conglomerate and breccia the fragments can be easily viewed