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Geology in the news today: Flooding continues in Colorado, with 5 confirmed dead and over 1,000 people still not located. The area under water is now equivalent in size to the state of Delaware. This is the roadway in front of the home of Lindsay Masters '06. See http://tinyurl.com/n7ekbwd for a National Geographic story on the linkage between these floods and global climate change. Chemistry of the Earth and an Introduction to Minerals I Only EIGHT elements make up >98% of the entire Earth: Iron (Fe) 34.8% Oxygen (O) 29.3% Silicon (Si) 14.7% Magnesium (Mg) 11.3% Sulfur (S) 3.3% Nickel (Ni) 2.4% Calcium (Ca) 1.4% Aluminum (Al)most abundant 1.2% NOTE that Fe is the in the Earth as a whole! CONTINENTAL CRUST is enriched in lighter elements Oxygen Silicon Aluminum Iron Calcium Magnesium Sodium Potassium O Si Al Fe Ca Mg Na K 45.2% of crust 27.2% 8.0% 5.8% 5.1% 2.8% 2.3% 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 text, pp. 53 & 54) 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). Smaller positive ions tend to fit in spaces between larger negative ions. 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 the strongest bonds holding minerals together. ALSO critically important 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 normally accommodated by addition of K+, Na+ and/or Ca++ 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 – these are the principal rock-forming minerals. 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 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. Chalcopyrite -> Cu Bornite -> Cu Pyrite – FeS2 – an important rock-forming mineral 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. 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. What would IT be good for? Other important oxides include: Corundum - Al2O3 Used to be mined extensively for abrasives now most important for the colored varieties ….. And the Oriental emerald All coloration is due to trace impurities ... Rubies …. sapphires 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???