Geosphere Materials Chapter 4

1. Geosphere MaterialsChapter 4

2. You will learn • Chemical Composition of the Geosphere • What Minerals Are: How They Are Made • Physical Properties of Minerals and Uses • How Minerals Change • How Rocks Form and Change • Uses for Rocks

3. Figure 4-2 Rocks are the most common geosphere materials, and can be fun, dangerous, beautiful, and useful.

4. The Geosphere’s Chemical Composition Elements Minerals Rocks Atoms Nucleus Protons (+) Neutrons (o) Electrons (-) Can’t be broken down into other substances 8 elements make up >98% of geosphere’s mass

5. Composition of the Geosphere • Crust can be directly observed and sampled • Composition of deep Earth—estimated from: • Density of Earth • Density variations from seismic velocities • Composition of meteorites • Assumptions of formation of solar system

6. Figure 4-4 Average Chemical Composition of the Geosphere Crust (a) The chemical makeup of the geosphere as a whole. (b) Chemical makeup of oceanic and continental crust.

7. Differences between Continental and Oceanic Crust • The combined percentage of iron and magnesium in oceanic crust (12.7%) is about 60% greater than that in continental crust (8.0%). • The percentage of calcium in oceanic crust (8.2%) is nearly twice that in continental crust (4.6%). • The percentage of potassium in continental crust (1.5%) is 15 times that in oceanic crust (0.1%). • The percentage of silicon in continental crust (28.3%) is 20% greater than that in oceanic crust (23.6%).

8. Figure 4-5Elements Bond Together by Transferring or Sharing Electrons(a) Ionic bonding (transfer) (b) Covalent bonding (sharing).

9. Common Rock-Forming Minerals in Geosphere • Quartz • Feldspar • Ferromagnesian minerals • Each is identified by a unique combination of physical and chemical properties: • Composition • Color • Luster • Hardness • Density (Specific Gravity)

10. Graphite is dark, soft, flaky. Diamond is very hard and commonly translucent Figure 4-6Diamond and Graphite Their internal structures explain why these two minerals have different crystal forms and physical properties, even though they’re both made solely of carbon.

11. Quartz: the Silicon-Oxygen Mineral, SiO2 Si4+ + 4 O2- = SiO4tetrahedron small Si ion between 4 larger O ions SiO4 tetrahedra can combine with others to form chains, rings, sheets, 3D frameworks

12. Quartz • SiO2 • Clear, white, gray, rose, smoky • H = 7 (on Moh’s scale of 1-10) • 6-sided prisms • Conchoidal fracture • Not chemically reactive Figure 4-8 Atomic Structure of Quartz 3D network of Si4+ and O2- tetrahedra that share oxygen atoms. The arrangement gives quartz crystals distinctive form.

13. Environmental/Health Risk • Tiny particles of quartz enter lungs • Particles get stuck in openings • Cause inflammation and nodular lesions • Lungs deteriorate • Shortness of breath, fever • Silicosis: pneumonoultramicroscopicsilicovolcanokoniosise.g., Hawk’s Nest, West Virginia

14. Granite • Granite—the material from which the faces on Mt. Rushmore were carved—is an aggregate of: • quartz • potassium feldspar • plagioclase feldspar • biotite FIGURE 4-9Granite: a Common Rock in Continental Crust

15. Feldspars • Potassium-rich KAlSi3O8 • Plagioclase (Na,Ca)(Si,Al)4O8 • White, gray, pinkish • H = 6 (on Moh’s scale of 1-10) • 4-sided prisms • 2 cleavages at 90º • Conchoidal fracture • Crystallizes over wide range of temperatures Figure 4-11 Potassium feldspar (a) and plagioclase feldspar (b) are very common rock-forming minerals. These have been broken along cleavages to form smooth, planar surfaces.

16. Weathering of Feldspars • Feldspars form at high temperatures and, hence, are not stable at Earth’s surface, where lower temperatures and pressures combine with interactions with the hydrosphere, atmosphere, and biosphere to cause minerals to change into minerals more stable at these conditions. • These changes are called Chemical and PhysicalWeathering • Two examples are: • Hydrolysis = reaction of water (H2O) with minerals to form new minerals (many with water in their atomic structures) • Dissolution = chemical (atomic) constituents are dissolved and removed

17. Feldspars Weather to ProduceClays and Micas Figure 4-13Micas are silicate minerals whose internal structures include a plane with very weak bonds. They easily break (cleave) into sheets along this plane. Biotite (dark mica) is an iron-bearing mineral. Muscovite (silvery mica) is potassium-rich. Figure 4-12 Clays have a layered atomic structure, not strongly bonded. Water can occupy space in the structure. They expand (wet) and contract (dry), thus making poor foundations.

18. Ferromagnesian Minerals Fe and Mg (similar in size, 2+ charge)—can substitute in mineral structures Olivine (Mg, Fe)2SiO4 Greenish, H=6, variable density conchoidal fracture (like quartz) Pyroxene (Mg, Fe, Ca)2 Si2O6 Dark, H=6, dense short rectangular prisms so have 2 cleavages at 90o Figure 4-15 Olivine (a) and Pyroxene (b) are ferromagnesian minerals that are common in mafic rocks like basalt and gabbro.

19. Weathering of Ferromagnesian Minerals • Olivines, pyroxenes, and amphiboles are even less stable at Earth’s surface than the feldspars. When they interact with the hydrosphere and atmosphere, they hydrolyze to form serpentine minerals. • Chrysotile is an elongate, fibrous serpentine mineral—the principal mineral in asbestos—and is heat-resistant and quite flexible. Figure 4-16 Chrysotile Ferromagnesian minerals hydrolyze to form many soft serpentine minerals. One of these, the fibrous serpentine mineral chrysotile, is the principal mineral in asbestos. Figure 4-18Tremolite A dangerous asbestiform amphibole. The elongate fibrous crystals of the amphibole mineral tremolite have caused serious health problems.

20. Ferromagnesian Minerals • Biotite K(Mg,Fe)3(Al,SiO3010)(OH)2 • Hydrated, black, H=3, mod. dense sheet structure (1 cleavage) • Hornblende (Ca,Na)2-3(Mg,Fe,Al)5 Si6(Si,Al)2O22(OH)2O6 • Dark, H=5-6, mod. dense elongate rectangular prisms have 2 cleavages @ 56 and 124° Figure 4-17 Biotite and hornblende (b) are hydrated ferromagnesian minerals.

21. Other Minerals, Sulfides, Oxides, and Carbonates • Sulfides—combinations of ions (especially metals with positive charges) with sulfur (2- charge) • Examples: • PbS Lead Sulfide Galena • ZnS Zinc Sulfide Sphalerite • FeS2 Iron Sulfide Pyrite • Some Earth systems concentrate sulfide minerals into metal-rich deposits—which are the principal source of metals through mining. • Processing of these minerals to extract the metals is implicated in many environmental issues. Figure 4-19 Pyrite or “Fool’s Gold”

22. Sulfides, Oxides, and Carbonates • Oxides—combinations of ions (especially metals with positive charges) with oxygen (2- charge) • TiO2 Titanium oxide Rutile • SnO2 Tin Oxide Cassiterite • Fe3O4 Iron Oxides Magnetite Fe2O3Hematite • FeO(OH)Goethite • Oxides tend to be more stable, less chemically reactive on Earth’s surface than other minerals. Like quartz, they commonly survive weathering and can become components of sand. • Several minerals at Earth’s surface react with oxygen. The positive ions in these minerals combine with oxygen to form oxide minerals. This chemical reaction is oxidation. An example is rust, combination of hematite, goethite. Figure 4-20 Oxidation of Fe-bearing minerals gives rocks, soils rusty color.

23. Sulfides, Oxides, and Carbonates Carbonates—combinations of positively charged ions (Ca2+,Mg2+,Fe2+) ions with negatively charged carbonate (CO32-) CaCO3 : Calcite (Ca,Mg)CO3: Dolomite • These minerals are generally soft (H = 3-4), light-colored, with good cleavages (often in 3 directions), making rhombs. • They are also prone to dissolve in acid, including acidic rain over time. • Landscapes (called Karst Terrains) underlain by calcite-rich rocks show many dissolution features (e.g., caves, sinkholes, disappearing streams).

24. Karst • Carbonate minerals generally form by precipitating from oceans (with a large concentration of Ca2+ and CO32-). Marine animals also precipitate carbonate minerals from seawater to make shells or other structures (e.g. coral reefs). • These die and sink to the ocean floor. Accumulations of carbonate material eventually form limestone. Figure 4-22 Dissolution of the Geosphere Produces Karst Terrain Dissolution of carbonate minerals leads to the formation of caves such as Mammoth Cave in Kentucky (a), hummocky landscapes (b), sinkholes that suddenly collapse (c).

25. Igneous Rocks • Crystallize/solidify from molten rock = magma • Felsic—Feldspar and silica (Si, Na, K) >63% SiO2 • most characteristic of continental crust • Mafic—Magnesium iron (ferric) (Fe, Mg, Ca) 45–55% SiO2 • most characteristic of oceanic crust—ferromagnesian minerals • Intermediate—common in subduction zones 55–63% SiO2 • Intrusive (plutonic)—erupt and crystallize rapidly, small crystals, basalt • Extrusive (volcanic)—cool slowly underground, large crystals, gabbro

26. (a)Basalt 30 micron thick slice of basalt photographed through a microscope using transmitted cross-polarized light. Light gray rectangular crystals are feldspar; olivine and pyroxene are variably colored irregular crystals. Individual crystals are extremely small, due to rapid cooling of the lava after eruption. (b)Gabbro White crystals are feldspar and dark crystals are pyroxene. Both the basalt and gabbro have the same composition, but the gabbro is coarser-grained than the basalt as a consequence of much longer cooling times. Figure 4-23

27. Oceanic crust includes: • deep-sea sediments • basalt lava flows • sheeted basalt dikes • gabbro intrusions • some ultramafic rocks Figure 4-24 Oceanic Crust Has a Well-defined Internal Structure.

28. Continental Crust • More compositionally diverse than oceanic crust • Range from mafic (lower) to felsic (upper) • Ave. composition is intermediate between these two end members, older, more structurally and compositionally complex • Originally basaltic—melted producing intermediate compositions • Today—oceanic crust is altered by hydrolysis with seawater— recrystallizes during subduction, releasing H2O, melting the crust • This melting forms intermediate (andesitic) magmas characteristic of subduction zones. These magmas are: • Often explosive • Release volatiles (H2O, CO2, H2S) • Andesite—intermediate/mafic, plagioclase + pyro

29. Rock Cycle Figure 4-25

30. Weathering • Set of physical and chemical processes that change rocks at Earth’s surface • Uplift causes rocks to be exposed, as outcrops, on the Earth’s surface • Expansion (from decompression) breaks rocks along fractures called joints • Physical Weathering—breaks the rocks into smaller pieces with higher surface area to volume ratio; principally from action of freezing water • Frost wedging: expansion of H2O in cracks breaks rock • Root wedging: growth of plant roots breaks rocks along cracks • Chemical Weathering—breaks down rocks and change composition • Hydrolysis • Oxidation • Dissolution

31. (a) Frost wedging: the repeated expansion of water as it freezes in cracks and disaggregates (breaks) rocks. • (b) Root wedging: growth of plant roots in cracks breaks rocks apart. • (c) Chemical weathering: processes such as hydrolysis, oxidation, dissolution, which decompose rocks. Figure 4-27 Weathering Processes

32. Erosion • Transportation of geosphere materials by movements of water, wind, and ice (glaciers)—primarily by gravity • Glaciers: • scrape material off valleys as they flow downslope • push material in front as they advance • deposits of rock debris from glaciers are called moraines • Streams and rivers: the principal movers of rock debris • Fast, deep streams may carry and move large boulders • Abrade and pluck material from the valley walls • Rock material rolled and bounced along the bottom of a stream/river is the bedload • Smaller sediments may be suspended, making the stream muddy

33. Sedimentary Rocks Sedimentation, Lithification • Sediment • Clastic sediments: composed of fragments of material • Chemical sediments: precipitate from solutions • Clastic Sediments • Transported—mainly by moving water (some by wind) from original source • Deposited—primarily in sedimentary basins, where water velocity drops • Clast size—depends on transport distance, velocity, strength gravel sand silt clay/mud

34. Figure 4-29Sedimentation(b) Rivers carry sediment to the coast. Figure 4-28Erosion (a) Sediment transport starts with rocks falling in steep terrain. (c) Fast-moving streams carry and abrade larger rocks.

35. Figure 4-30 Clastic Sedimentary RocksWhen sediments become deeply buried, they lithify. (a) Muddy sediment turns into shale. (b) Sand becomes sandstone. (The rusty stains in this specimen define individual layers or beds.) (c) Gravel forms rocks called conglomerate. Figure 4-29(a) Clastic sediments range in size from tiny clay particles to sand and gravel.

36. Chemical Sedimentary Rocks • These minerals generally precipitate where evaporation has increased their concentration in seawater, so the rocks they form are called evaporites. • Limestone—Most common chemical sediment is calcium carbonate, the mineral calcite (CaCO3). Where calcite is buried and lithified it becomes limestone. There are many types: • Fossiliferous • Oolitic • Crystalline • Microcrystalline (micrite) • Gyprock—mineral gypsum (CaSO4) • Rock Salt—minerals halite (NaCl) and sylvite (KCl)

37. Figure 4-31 Limestone: A Marine Sedimentary Rock Limestone is derived from the mineral calcite, a form of calcium carbonate. Calcite that precipitates on the seafloor, or accumulates there in the remains of marine organisms, becomes limestone when it is lithified.

38. Metamorphism • Rocks changed from higher temperature and pressure. Any rock can become metamorphosed (igneous, sedimentary, metamorphic). • minerals formed at the surface not stable at higher T and P • recrystallize to form minerals stable at higher T and P • recrystallization largely involves dehydration reactions • new minerals grow in orientations influenced by P—metamorphic textures

39. Metamorphism (cont.) • Typical metamorphic rocks: • Schist: usually contains flaky mica minerals—oriented parallel to one another • foliation = strongly 2D sheeted structure, termed schistosity • sedimentary rocks (shale, sandstone) are examples of schist protoliths • Gneiss: contains discontinuous layers (called lenses) of larger minerals (generally quartz and feldspar) separated by finer-grained, schistose layers • forms at higher T and P than many schists • gneiss can form from any rock, but many form from clastic sedimentary rocks • Marble:metamorphosed limestone (mineral still is calcite) • the original calcite minerals have been recrystallized • tend to be larger than the original ones in the limestone

40. Figure 4-32 Metamorphic Rocks In schist(a), generally formed from sedimentary rocks like shale or sandstone, crystals of new minerals such as biotite are oriented parallel to each other. This arrangement gives the rock a well-developed foliation. In gneiss(b), typically formed at higher temperatures and pressures than schist, new minerals tend to be coarser and segregated into discontinuous layers and lenses. The folded layers in this gneiss are a few to several centimeters across (about 1–10 in).

41. Using Rocks • Commercial and residential buildings • Highways, bridges, sidewalks, and parking lots • Factories and power generation facilities • Water storage, filtration, and delivery systems • Wastewater collection and treatment systems

42. FIGURE 4-36 Distribution of Aggregate Mining Aggregate mining operations can be found near most communities in the United States.

43. Aggregate • Aggregate = sand, gravel, and crushed stone—“common rock” • incorporated into cement and asphalt • spread on roadways and building sites to help stabilize the ground • Our need for aggregate is increasing, especially for basic infrastructure • bridges, highways, transit construction, etc. • cheap to mine and process • but transporting is costly Figure 4-35 Past and Future Use of Aggregate Our need for aggregate, especially crushed stone, is increasing rapidly. It is estimated that by 2020 we will be using more than twice as much as we did in 1960.

44. Issues with Aggregate Mining • Physical disturbances • Aggregate must be physically removed from its source—leaving physical disturbances such as quarries or pits, the removing of natural vegetation • Mitigate by developing visibility barriers, ensuring well-planned and orderly operations, and reclaiming areas as operations proceed • Slope contouring, new soil, revegetation (reclamation) • Aggregate pits and quarries can become lakes for recreation and wildlife habitat • Disturbed terrain can become parks, gardens, or even golf courses

45. Issues with Aggregate Mining (cont.) • Dust and noise • Aggregate mining, breaking up rocks blasting, hauling, and crushing • Dust can cause respiratory illnesses • Air quality monitoring and compliance with regulations required • Noise from blasting and equipment operations a significant concern • Congestion and safety

46. Aggregate Mining in Your Neighborhood • How would you answer the following questions? • Do you think that the annual and per capita consumption of aggregate accurately reflects your use of these resources? • What do you think the future aggregate needs of the U.S. are going to be? What are the more important factors that influence these needs? • Where do you think new aggregate resources should come from? • Do you think aggregate mining should take place in your community? • Do you think that mitigation measures such as reclamation can satisfactorily address the environmental concerns associated with aggregate mining?