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Geology in the news: Representatives of the Maldives, Kiribati, the Seychelles, Palau, and other low-lying island nations are going to mount an aggressive campaign at the U.N. General Assembly when it reconvenes on Sept. 28th. Their goal will be to get participating nations at the Paris global-warming conference in December to adopt tough antiwarming standards, in hopes of preserving their nations' very existence. See http://tinyurl.com/ohabjwo This is why the HVO has placed Mauna Loa on a "yellow alert." On a more local front: There is now a Geology Help Center – in Mudd 411. Advanced Geology majors will be there to provide help on Sundays and Tuesdays, from 7-9 p.m. On weeks with GE141 exams, they will have extra Monday shifts, also 7-9 p.m. June Li, Oriana Battifarano, and Lauren McCarthy will be there to help! Plate Tectonics Recap The Earth's surface is underlain by relatively RIGID tectonic PLATES of lithosphere, resting atop plastic, deformable aesthenosphere. Tectonic plates DIVERGE at extensional zones The process is driven by CONVECTION in the mantle, resulting in SLAB PULL at subduction zones, and SLAB PUSH at areas of mantle upwelling. The Mid-Ocean Rise and Ridge System (MORRS) marks the areas where plate divergence is taking place. Flow rates are measured in cm/year (typically 2-15 cm/yr) Plate Tectonics Recap II There are three kinds of Zones of Convergence where tectonic plates come together. Oceanic subduction beneath a continental margin – e.g., western South America, or the Pacific Northwest of the U.S.A., or Kamchatka Oceanic subduction beneath other oceanic crust, creating an island arc system – e.g., the Aleutian, Kuril, Japanese or Philippine Islands, as well as the Antilles, Sumatra & Java Continent-continent collisions, as in India-Asia. Plate convergence is what creates most mountains – and is why major mountain ranges are linear features. Plate Tectonics Recap III Hawaii is NOT on a plate margin, but owes its origin to the Pacific Plate moving NW over a mantle plume, or "hot spot" that produces volcanism. The San Andreas Fault of California is a transform fault, in which the North American and Pacific Plates are sliding sideways past each other. This is along an offset in the East Pacific Rise, part of the MORRS. Accreted terranes are blocks of land that had their own geologic history, but got "stuck onto" the continent by convergent plate motions. Moving right along ... Chemistry of the Earth and an Introduction to Minerals Only EIGHT elements make up >98% of the entire Earth: Iron (Fe) Oxygen (O) Silicon (Si) Magnesium (Mg) Sulfur (S) Nickel (Ni) Calcium (Ca) Aluminum (Al) 34.8% 29.3% 14.7% 11.3% 3.3% 2.4% 1.4% 1.2% NOTE that Fe is the most abundant element in the Earth as a whole! CONTINENTAL CRUST is enriched in lighter elements Oxygen Silicon Aluminum Iron Calcium Magnesium Sodium Potassium O 45.2% of crust Si 27.2% Al 8.0% Fe 5.8% Ca 5.1% Mg 2.8% Na 2.3% K 1.7% O + Si = ~72% of the crust; SILICATE minerals are far and away the dominant group on Earth. Quartz (SiO2) is one of the most common minerals (see fig. 3.3, p. 76; fig. 3.4d, p. 79; fig. 3.7a, p. 80) ELEMENTS COMBINE via chemical bonding a) IONIC BONDING occurs when an element gains or loses an electron to have a complete outer shell; this occurs when elements have many or very few electrons in outer shell. (e.g., K, Na, Cl) Size of elements is also a factor in mineral formation. Positive ions (cations) are usually smaller than negative ions (anions). The smaller cations tend to fit in spaces between larger anions. Structure of halite - NaCl showing ionic bonding at work b) COVALENT BONDING occurs when elements have moderate numbers of electrons (e.g., Si, C, Fe+++), so it's easier for them to share electrons than to strip or fill an outer shell per each atom. Structure of ethane, a gas, showing covalent C-C and C-H bonding Water is also held together by covalent bonds Covalent bonding forms strong bonds holding minerals together. In metallic bonding, important in many native elements (like gold or copper), the metallic ions form a crystal lattice that is stabilized by a "sea" of electrons that are free to move from one ion to another. These free electrons are why metals are able to convey an electrical current! Critically important in many minerals is IONIC SUBSTITUTION (the substitution of one ion for another of similar size and the same or a close electrical charge) TWO are extremely common and VERY important : 1. This can be illustrated in the structure of the rock-forming mineral OLIVINE: 2. THIS pair of ions is critical - because both silicon and aluminum are so abundant. This characterizes THE major mineral group that makes up over half the entire crust - the feldspars! HOWEVER, this also sets up a charge imbalance! This is accommodated by addition of K+, Na+, Ca++ and other ions to the minerals. Soooo, what IS a mineral, anyway? 1. Naturally occurring 2. Inorganic solid 3. Has a constant chemical composition, or one varying within defined, set limits 4. Has a crystalline (ordered) internal structure. ( This is reflected in the crystal form! ) QUESTION: Is the January ice on Johnson Pond a mineral ??? Is wood a mineral ? Is glass a mineral ? Critical to remember is that ALL minerals are stable ONLY under specific temperature-pressure conditions! Minerals that have both silicon and oxygen in them are the silicate minerals. These comprise 95% of the crust - we'll cover them last, but in some detail. The NON-silicate minerals (i.e., all the others) are, save the carbonates, most important for their economic significance. 1. The first group is the simplest group: Native elements . These are comprised of a single element, not in combination with will denote those you'll see in lab! anything else. Gold * Diamonds Graphite Native copper Native silver Native sulfur 2. Second group is the Sulfides. Many are major ores. These are comprised of a metal plus sulfur. * * Pyrite - NOT an ore Chalcopyrite Cu Bornite Cu + Cinnabar Hg Sphalerite Zn …. * Galena Pb Molybdenite Mo * Sulfide minerals, and Native Sulfur (from coal seams) give rise to , an environmental disaster if left untreated. Though some of this acidic drainage occurred naturally before mining began, access to the minerals responsible was greatly enhanced by mining activities. Some of you may remember the acid mine drainage spill into the Animas River of Colorado this past summer. 3. Third group is the Oxides and Hydroxides. Many of these are also major ores. These are comprised of a metal plus either oxygen or an (OH) group, or both. * * * Magnetite Hematite Limonite The three major ores of iron , mined worldwide Bauxite is a blend of AlOOH, Al (OH)3, and other aluminum oxides and hydroxides A. Is Bauxite a mineral? B. Why is this specimen red? C. For what would IT be useful? * Other important oxides include: Corundum - Al2O3 * Used to be mined extensively for abrasives - now most important for the colored varieties ….. Rubies …. sapphires And the Oriental emeralds All coloration is due to trace impurities ... 4. The fourth group is the Halides - made up of a metal plus a halogen - usually Fluorine or Chlorine * Halite - NaCl Halite and Sylvite show well the influence of internal structure on the ultimate shape of the mineral grains. Sylvite - KCl Fluorite - CaF2 - is also a very important halide mineral * As you can guess from these pictures, fluorite can be practically ANY color! WHY???