Earth Materials— Minerals and Rocks

1. Chapter 2 Earth Materials—Minerals and Rocks

2. Earth Materials – Minerals • Gemstones and other minerals, • such as gold, • have fascinated people for thousands of years • and have been supposed • to have mystical or curative powers • Minerals have many essential uses • in industrial societies • Minerals are the basic units • that make up most of Earth’s materials

3. Earth Materials – Rocks • With only a few exceptions rocks • are solid aggregates of minerals • Rocks too find many uses • rocks crushed for aggregate in cement and for roadbeds • sawed and polished rocks for tombstones, monuments, mantle pieces and counter tops • Even the soils we depend on • for most of our food • formed by alteration of rocks

4. Rocks • Granite cliff of El Capitan, Yosemite, California • rises 900 m above the valley floor • highest unbroken cliff in the world

5. Minerals • Geological definition of a mineral: • naturally occurring • crystalline solid • crystallinemeans that minerals • have an ordered internal arrangement of their atoms • minerals have a narrowly defined chemical composition • and characteristic physical properties such as • density • hardness • color...

6. Minerals Minerals on display • at the California Academy of Sciences in San Francisco

7. Earth Materials • Some materials formed by the Earth • are interesting and attractive • such as this metamorphic rock • from the shoreline of Lake Superior at Marquette, Michigan

8. Matter and Its Composition • Matter • is anything that has mass and occupies space • exists as solids, liquids, and gases • consist of elements and atoms • Element • is a chemical substance • that cannot be chemically decomposed • into simpler substances • and is composed of tiny particles called atoms

9. Atoms • Atoms are the smallest units of matter • that retain the characteristics of the element • Atoms have • a compact nucleus containing • protons – particles with a positive electrical charge • neutrons – electrically neutral particles • particles orbiting the nucleus • electrons – negatively charged particles

10. Structure of an Atom • The dense nucleus of an atom • consisting of protons and neutrons • is surrounded by a cloud of orbiting electrons

11. Atoms • Atomic number = the number of protons • Atomic mass number = number of protons + number of neutrons • The number of neutrons in an atom • may vary

12. Isotopes • The different forms of an element’s atoms • with varying numbers of neutrons • are called isotopes. • Different isotopes of the same element • have different atomic mass numbers • behave the same chemically • Isotopes are important in radiometric dating

13. Carbon Isotopes • Carbon atoms (with 6 protons) • have 6 neutrons = Carbon 12 (12C) • have 7 neutrons = Carbon 13 (13C) • or have 8 neutrons = Carbon 14 (14C) • thereby making up three isotopes of carbon.

14. Electrons and Shells • Electrons orbit the nucleus in one or more shells • The outermost shell participates • in chemical bonding • and contains up to 8 electrons • Noble gas configuration of 8 electrons • or 2 for helium • completes the outermost shell • Other atoms attain • a noble gas configuration • in the process of bonding

15. Bonding and Compounds • Bonding • the process whereby atoms join to other atoms • Compound • a substance resulting from the bonding • of two or more elements • Oxygen gas (O2) is and element • Ice is a compound • made up of hydrogen and oxygen (H2O) • Most minerals are compounds

16. Ionic Bonding • Ion • an atom that has gained or lost one or more electrons • and thus has a negative or positive charge • One way for atoms to attain the noble gas configuration • is by transferring electrons, producing ions • Ionic bonding • attraction between two ions of opposite charge

17. Covalent Bonding • Another way for atoms • to attain the noble gas configuration • is by sharing electrons • Covalent bonding • results from sharing electrons shared electrons

18. Minerals—The Building Blocks of Rocks • A mineral’s composition is shown by a chemical formula • a shorthand way of indicating how many atoms of different kinds it contains • Quartz consists of 1 silicon atom for every 2 oxygen atoms • Quartz: SiO2 • Ratio: 1: 2 • Orthoclase consists of 1 potassium, 1 aluminum, and 3 silicon for every 8 oxygen atoms KAlSi3O8 1: 1: 3: 8

19. Native Elements • A few minerals consist of only one element. • They are not compounds. • They are known as native elements. • Examples: • gold – formula: Au • diamond – formula: C

20. Crystalline Solids • By definition, minerals are crystalline solids • with atoms arranged in a specific 3D framework • If given enough room to grow freely, • minerals form perfect crystals with • planar surfaces, called crystal faces • sharp corners • straight edges

21. Narrowly Defined Chemical Composition • Some minerals have very specific compositions • examples are halite (NaCl) or quartz (SiO2) • but others have a range of compositions • because one element can substitute for another • if the atoms of the two elements have • the same electrical charge • and are about the same size • example: olivine • (Mg,Fe)2SiO4 • iron and magnesium substitution in any proportion

22. Mineral Properties • Mineral properties are controlled by • Chemical composition • Crystalline structure • Mineral properties are particularly useful • for mineral identification and include: • color • streak • luster • crystal form • cleavage • fracture • hardness • specific gravity

23. How Many Minerals Are There? • More than 3500 minerals are known • Only about 2 dozen are particularly common • Many others are important resources • Mineral groups: • minerals with the same negatively charged ion or ion group • belong to the same mineral group • Most minerals in the crust • belong to the group called silicates

24. Silicates • Silicates are minerals containing silica • Si and O • They make up perhaps 95% of Earth’s crust • and account for about 1/3 of all known minerals • The basic building block of silicates • is the silica tetrahedron • which consists of one silicon atom • surrounded by four oxygen atoms

25. Types of Silicates • Silica tetrahedra can be • isolated units bonded to other elements • arranged in chains (single or double) • arranged in sheets • arranged in complex 3D networks

26. Types of Silicates • Ferromagnesian silicates • contain iron (Fe), magnesium (Mg), or both • Nonferromagnesian silicates • do not contain iron or magnesium

27. Ferromagnesian Silicates • augite, a pyroxene-group mineral • olivine • Common ferromagnesian silicates include biotite mica • Hornblende, an amphibole-group mineral

28. Nonferromagnesian Silicates QuartzPotassium feldspar Plagioclase feldspar Muscovite

29. Other Mineral Groups • Carbonates • minerals with carbonate ion (CO3)-2 • as in calcite (CaCO3), • found in limestone • and dolomite [CaMg(CO3)2], • found in dolostone • Other mineral groups are important, • but more as resources • than as constituents of rocks

30. Rock-Forming Minerals • Most rocks are solid aggregates • of one or more minerals • Thousands of minerals occur in rocks, • but only a few are common • and calledrock-forming minerals • Most rock-forming minerals are silicates, • but carbonates are also important • Accessory minerals are present in small amounts • and are ignored in classifying rocks

31. Rock Cycle • The rock cycle is a pictorial representation • of events leading to • the origin, destruction, change • and reformation of rocks • Rocks belong to 3 major families • igneous • sedimentary • metamorphic • The rock cycle shows • how these rock families are interrelated • and can be derived from one another

32. Rock Cycle Lava Pyroclastic material

33. Igneous Rocks • All igneous rocks • cool and crystallize from magma, • solidify from lava, • or consolidate from pyroclastic materials • Magma is molten material • below the surface • Lava is molten material on the surface • Pyroclastic materials • are particles such as volcanic ash

34. Lava Pyroclastic material Igneous Part of the Rock Cycle

35. Categories of Igneous Rocks • Extrusive or volcanic rocks • formed at the surface • from lava or pyroclastic materials • Intrusive or plutonic rocks • formed from magma injected into the crust • or formed in place in the crust • Plutons are intrusive bodies • consisting of plutonic rock

36. Plutons

37. Igneous Rock Textures • Texture • is the size, shape and arrangement • of crystals, grains and other constituents of a rock • Igneous rocks have 4 textures • that relate to cooling rate of magma or lava

38. 4 Cooling-Rate Textures • phaneritic, • with visible grains • cooled slowly • aphanitic, • with grains too small to see without magnification • cooled quickly • porphyritic, • with larger grains surrounded by a finer-grained groundmass • cooled slowly first, then more quickly • glassy, • with no grains • cooled too quickly for minerals to grow

39. Igneous Rock Textures • Other textures reveal further details • of the formation of the rock • Vesicular texture, with holes (vesicles), • indicates the rock formed • as water vapor and other gases • became trapped during cooling of lava • Pyroclasticor fragmental texture, • containing fragments, • formed by consolidation of volcanic ash • or other pyroclastic material

40. Igneous Rock Textures Rapid cooling Aphanitic texture Slow cooling Phaneritic texture 2-stage cooling Porphyritic texture

41. Igneous Rock Textures Glassy texture cooling was too rapid for mineral growth Vesicular texture gasses trapped in cooling lava Pyroclastic texture particles fragmented during eruption

42. Classifying Igneous Rocks • Texture and composition are the criteria • used to classify most igneous rocks • Composition categories are based on silica content • felsic (>65% silica) • intermediate (53-65% silica) • mafic (45-52% silica) • More felsic magmas have higher Na, K, Al • More mafic magmas have higher Ca, Fe, Mg

43. Classifying Igneous Rocks

44. Common Igneous Rocks Basalt Gabbro Andesite Diorite

45. Common Igneous Rocks Rhyolite Granite

46. Pumice Obsidian Volcanic breccia Tuff/welded tuff Felsic Mafic Classifying Igneous Rocks with Special Textures Texture Vesicular Glassy Pyroclastic or Fragmental Composition

47. Igneous Rocks with Special Textures Tuff has pyroclastic texture. Pumice is glassy and extremely vesicular.

48. Sedimentary Rocks • Sedimentary rocks form • by the lithification of sediment • In the rock cycle, sediment originates when: • mechanical and chemical weathering • breaks rocks down into smaller particles • and into solution • Transport removes sediment • from its source area • and carries it elsewhere • Running water, glaciers, wind and waves • transport sediment • Deposition involves settling of particles, • and chemical and biological extraction of minerals from solution

49. Sedimentary Part of the Rock Cycle

50. Lithification • Lithification means • turning loose sediment into rock • Lithification occurs by • burial • when additional sediment accumulates on top • compaction • reduction of the amount of pore space between particles • because of the weight of overlying sediment • cementation • precipitation of minerals within pores • that effectively binds sediment together • calcium carbonate (CaCO3) cement is common • silica (SiO2) cement is common • iron oxide (Fe2O3) cement is less common