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Minerals and Rocks

Minerals and Rocks

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Minerals and Rocks

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  1. Chapter 2 Minerals and Rocks

  2. Earth Materials – Minerals • Some 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 • Rocks also have many uses: • rocks crushed for aggregate in cement and for roadbeds • sawed and polished rocks for tombstones, monuments, mantle pieces and countertops • Even the soils we depend on • for most of our food • are formed by alteration of rocks

  4. Rocks • Mountains around Tenaya Lake in Yosemite National Park • Made of granite • Granite is composed of quartz and feldspar minerals

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

  6. 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

  7. Matter and Its Composition • Matter • anything that has mass and occupies space • exists as solids, liquids, gases, and plasma • consists of elements and atoms • Element • a chemical substance • composed of tiny particles called atoms

  8. 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 outside the nucleus • electrons – negatively charged particles

  9. Atoms • Atomic number = the number of protons • Atomic mass number = number of protons + number of neutrons • The number of neutrons in nucleus of an element may vary

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

  11. Carbon Isotopes • Three isotopes of carbon (all with 6 protons) • 6 neutrons = Carbon 12 (12C) • 7 neutrons = Carbon 13 (13C) • 8 neutrons = Carbon 14 (14C)

  12. Electrons and Shells • Electrons lie outside the nucleus in one or more shells • The outermost shells are involved • in chemical bonding • and contain up to 8 electrons • Noble gas configuration of 8 electrons • or 2 for helium • have complete outer shells • and are stable • Other atoms attain • a noble gas configuration • through the process of bonding

  13. 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 an element • Ice (H2O) is a compound • made up of hydrogen and oxygen atoms • Most minerals are compounds

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

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

  16. Minerals • Geological definition of a mineral: • naturally occurring • crystalline solid • crystallinemeans that minerals • have atoms arranged in specific 3-dimensional frameworks • inorganic • minerals have a narrowly defined chemical composition • and characteristic physical properties such as • density • hardness

  17. 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 molecules consist of 1 silicon atom and 2 oxygen atoms • Quartz: SiO2 • Ratio: 1: 2 • Orthoclase molecules consists of 1 potassium, 1 aluminum, 3 silicon, and 8 oxygen atoms KAlSi3O8 1: 1: 3: 8

  18. Native Elements • A few minerals consist of only one element. • They are not compounds. • They are known as native elements. • Examples: • Gold: Au • Diamond: C

  19. 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

  20. Narrowly Defined Chemical Composition • Some minerals have very specific compositions • Examples: halite (NaCl), quartz (SiO2) • Other minerals 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

  21. 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

  22. 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

  23. Silicates • Silicates are minerals containing silica • Si and O • These minerals make up almost 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

  24. 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

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

  26. Ferromagnesian Silicates • Common ferromagnesian silicates include

  27. Nonferromagnesian Silicates

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

  29. Rock-Forming Minerals • Most rocks are solid aggregates • of one or more minerals • Hundreds 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

  30. 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

  31. Rock Cycle

  32. 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

  33. Lava Pyroclastic material Igneous Part of the Rock Cycle

  34. 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

  35. Plutons

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

  37. Igneous Rock Textures

  38. Cooling-Rate Textures • phaneritic, • with visible grains • cooled slowly • aphanitic, • with grains too small to see without magnification • cooled quickly • porphyritic, • with larger grains (phenocrysts) surrounded by a finer-grained groundmass • cooled slowly intrusively, then expelled onto the surface • 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 • Pyroclastic or fragmental texture, • containing fragments, • formed by consolidation of volcanic ash • or other pyroclastic material

  40. Igneous Rock Textures

  41. Classifying Igneous Rocks • Texture and composition are the criteria • used to classify most igneous rocks • Composition categories are based on mineral composition • FELSIC, light colored, >65% silica • INTERMEDIATE, 53-65% silica • MAFIC, dark colored, 45-52% silica • ULTRAMAFIC, <45% silica

  42. Classifying Igneous Rocks

  43. Common Igneous Rocks Basalt Gabbro Andesite Diorite

  44. Common Igneous Rocks Rhyolite Granite

  45. Classifying Igneous Rocks with Special Textures

  46. Igneous Rocks with Special Textures Outcrop with basalt underlain by tuff Pumice is glassy and extremely vesicular.

  47. Sedimentary Rocks • Sedimentary rocks form • by the lithification of sediment • In the rock cycle, sediment originates when • mechanical and chemical weathering • disintegrate and decompose rocks at the surface • Transport removes sediment • from its source area and carries it elsewhere • Sediments accumulate in deposits, • or as minerals that precipitate from solution • or that organisms extract from solution.

  48. Sedimentary Part of the Rock Cycle

  49. Lithification • Lithification means • converting sediment into sedimentary rock • Lithification occurs by • compaction • Pressure exerted by overlying sediments • reduction of the amount of pore space between particles • cementation • precipitation of minerals within pores • effectively binds sediment together • calcium carbonate (CaCO3) cement is common • silica (SiO2) cement is common • iron oxide or iron hydroxide (Ex: Fe2O3) cement is less common

  50. Categories of Sedimentary Rocks • Detrital sedimentary rocks • consist of solid particles • derived from preexisting rocks (detritus) • Chemical sedimentary rocks • consist of minerals derived from materials in solution and • extracted by either • inorganic chemical processes • or by the activities of organisms • subcategory biochemical sedimentary rocks, in which • the activities of organisms are important