Rocks: Materials of the Solid Earth Chapter 3

1. Rocks: Materials of the Solid EarthChapter 3 Earth Science, 13e Stanley C. Hatfield, Southwestern Illinois College

2. Objectives • What is the rock cycle and why is it important? • What are the three groups of rocks and the geologic processes involved in the formation of each?

3. Objectives • How does magma differ from lava? • What two criteria are used to classify igneous rocks? • How does the rate of cooling influence the crystal size of minerals in igneous rocks?

4. Objectives • What are the names and environments of formation for some common detrital and chemical sedimentary rocks? • What processes change sediment into sedimentary rock? • What are two characteristics of sedimentary rock?

5. Objectives • What are metamorphic rocks and how do they form? • What are the agents of metamorphism? • What are the names, textures and environments of formation for some common metamorphic rocks?

6. The rock cycle

7. Rock cycle • Shows the interrelationships among the three rock types • Earth as a system: the rock cycle • Magma • Crystallization • Igneous rock • Weathering, transportation, and deposition

8. Rock cycle • Earth as a system: the rock cycle • Sediment • Lithification • Sedimentary rock • Metamorphism • Metamorphic rock • Melting • Magma

9. Rock cycle • Earth as a system: the rock cycle • Full cycle does not always take place due to “shortcuts” or interruptions • e.g., Sedimentary rock melts • e.g., Igneous rock is metamorphosed • e.g., Sedimentary rock is weathered • e.g., Metamorphic rock weathers

10. The rock cycle

11. Igneous rocks • Form as magma cools and crystallizes • Rocks formed inside Earth are called plutonic or intrusive rocks • Rocks formed on the surface • Formed from lava (a material similar to magma, but without gas • Called volcanic or extrusive rocks

12. Igneous rocks • Crystallization of magma • Ions are arranged into orderly patterns • Crystal size is determined by the rate of cooling • Slow rate forms large crystals • Fast rate forms microscopic crystals • Very fast rate forms glass

13. Igneous rocks • Classification is based on the rock’s texture and mineral constituents • Texture • Size and arrangement of crystals • Types • Fine-grained – fast rate of cooling • Coarse-grained – slow rate of cooling • Porphyritic (two crystal sizes) – two rates of cooling • Glassy – very fast rate of cooling

14. Igneous Rock Textures

15. Glassy Texture

16. Obsidian exhibits a glassy texture

17. Fine-grained igneous texture

18. Porphyritic igneous texture

19. Course-grained igneous texture

20. Igneous rocks • Classification is based on the rock’s texture and mineral constituents • Mineral composition • Explained by Bowen’s reaction series which shows the order of mineral crystallization • Influenced by crystal settling in the magma

21. Classification of igneous rocks

22. Common Igneous Rocks

23. Bowen’s reaction series

24. Igneous rocks • Naming igneous rocks • Granitic rocks • Composed almost entirely of light-colored silicates – quartz and feldspar • Also referred to as felsic: feldspar and silica (quartz) • High silica content (about 70 percent) • Common rock: granite, rhyolite

25. Intrusive vs. Extrusive

26. Igneous rocks • Naming igneous rocks • Andesitic rocks • Midway between granitic and basaltic • Mostly amphibole (dark) and plagioclase feldspar (light) • Also referred to as intermediate • Common rock: diorite, andesite

27. Intrusive vs. Extrusive

28. Igneous rocks • Naming igneous rocks • Basaltic rocks • Contain substantial dark silicate minerals and calcium-rich plagioclase feldspar • Also referred to as mafic: magnesium and ferrum (iron) • Common rock: gabbro, basalt

29. Intrusive vs. Extrusive

30. Igneous rocks • Naming igneous rocks • Ultramafic (dark) – olivine, pyroxene • Rare at Earth’s surface but peridotite is believed to be a primary constituent of Earth’s mantle.

31. Bowen’s Reaction Series • N. L. Bowen (early 20th century) discovered that magma crystallizes over a range of temperatures. • Each rock group consists of minerals that crystallize in same temperature range.

32. Bowen’s Reaction Series • Continuous : • When plagioclase is very hot it is calcium rich, when it cools it becomes sodium rich • Temperature-induced chemical reaction • Discontinuous: • At a certain temperature a magma might produce olivine, but if that same magma was allowed to cool further, the olivine would "react" with the residual magma, and change to the next mineral on the series.

33. Sedimentary rocks • Form from sediment (weathered products) • About 75 percent of all rock outcrops on the continents • Used to reconstruct much of Earth’s history • Clues to past environments • Provide information about sediment transport • Rocks often contain fossils

34. Sedimentary rocks • Economic importance • Coal • Petroleum and natural gas • Sources of iron and aluminum

35. Sedimentary rocks • Classifying sedimentary rocks • Two groups based on the source of the material • Detrital rocks • Material is solid particles • Classified by particle size • Common rocks include • Shale (most abundant) • Sandstone • Conglomerate

36. Classification of sedimentary rocks

37. Conglomerate vs. breccia

38. Sandstone vs. siltstone

39. Shale with plant fossils

40. Once a rock(er), now a fossil…

41. Sedimentary rocks • Classifying sedimentary rocks • Particle size provides information about env’t in which sediment was deposited • Stronger currents (air, water, glaciers) carry larger particles • Sand – less energy • Silts/clays settle slowly  associated w/quiet waters • Can be a mix of particle sizes (ex: sandy siltstone) • Mineral composition • Ex: quartz sandstone

42. Sedimentary rocks • Classifying sedimentary rocks • Two groups based on the source of the material • Chemical rocks • Derived from material that was once in solution and precipitates to form sediment • Directly precipitated as the result of physical processes, or • Through life processes (biochemical origin)

43. Sedimentary rocks • Classifying sedimentary rocks • Two groups based on the source of the material • Chemical rocks • Common sedimentary rocks • Limestone – the most abundant chemical rock • Microcrystalline quartz (precipitated quartz) known as chert, flint, jasper, or agate • Evaporites such as rock salt or gypsum • Coal

44. Biochemical Sedimentary Rock Coquina B. Seashells @ Sanibel Island, Florida

45. Biochemical Sedimentary Rock White Chalk Cliffs, Sussex England (chalk is soft, porous limestone)

46. Inorganic Limestone • Chemical changes, high water temp raise CaCO3 concentration to the point that it precipitates. • Chert – dense, hard rocks made of microcrystalline quartz • Agate – banded • Flint – dark color comes from organic matter • Jasper – red due to iron oxide • Arrowheads, etc. often made from chert

47. Chert

48. Evaporite Deposits • Halite, gypsum (used in drywall, plaster) • Salt flats form when water evaporates, precipitates remain

49. Coal Formation • No oxygen present to allow for complete decay of plant material (stagnant swamp for example)