Lecture Outline Wednesday - Monday January 24-29, 2018

Transcription

1 Lecture Outline Wednesday - Monday January 24-29, 2018 Lecture Quiz Friday January 26, 2018 Where: Webster 16 Type of question: Multiple choice and identification of features from slides 3-4 short answer questions Length 20 questions, computer graded (20pts) Covers material thru Wed. Jan. 24 Questions?? Finish lecture notes on Chapter 2 Review Key Points for today What is a mineral? What causes atoms to combine to form minerals? What conditions are necessary for minerals to form? What are some of the physical properties that we can test for to help identify/name a mineral? What is a Mineral? crystalline solid - atoms are arranged in a (ex: a cube) Specific chemical compound - contains particular elements in a set ratio. H 2 O has a set ratio. Is it a mineral? What about mineral water? Ice? FeS 2 pyrite (fools gold) Atoms Composed of a nucleus Protons (+) Neutrons (no charge) Electrons (- charge) orbit the nucleus in shells (orbitals). Atomic Number = # of in the nucleus. Ex: Carbon atom (6) Atomic Mass = # of +. Ex: Carbon atom (6 protons, 6 neutrons: 12) Protons atomic mass 1 Neutrons atomic mass 1 Electrons atomic mass ~ 0 Isotopes = the # of neutrons may change All carbon atoms have 6 protons (atomic number). The atomic mass = 6 protons + 6 neutrons = 12 Ex: Carbon 13 (7 neutrons) and Carbon 14 (8 neutrons) are all isotopes of Carbon. Electrons Electrons are attracted to and form an electron cloud around the nucleus. For stable atoms, the number of electrons = the number of protons. Ion, is an atom which has. ex. Na + (cation) and Cl - (anion) So how does this make minerals? Minerals form when atoms transfer or share electrons to fill there shells = chemical bonding.

2 Chemical Bonding Atoms combine (bond) by losing, gaining or sharing electrons to form minerals. Ionic Bonding of electrons. Form when shells are nearly empty or nearly full. bond. Covalent Bonding of Electrons Form when shells are about half full bond Ionic bonding Covalent bonding Carbon has 4 electrons but would like to have eight. Covalent bonding: Each atom shares electrons Every C atom sees 8 electrons. (fills the electron shell) -- Diamond! How does this affect the physical properties of diamonds? See Table 3.4 for relationship of property to composition and crystal structure. What Mineral Will Form? (depends on) Available Elements Ionic Substitution Conditions of Crystallization Polymorphs (same ) Ex: Diamond and Graphite How do Minerals Form? Chemical reactions between elements. Crystallization the growth of a solid from a gas or liquid whose constituents come together in the proper chemical proportions and crystalline arrangement What conditions cause minerals to form? Lower the temperature of a liquid below its freezing point Liquids evaporate from a solution forming a supersaturated solution and results in precipitate When atoms and ions in a solid become mobile and rearrange themselves at high temperature (>250 C) Mineral Identification Different minerals look different because they have different physical properties. This is a result of chemical composition (formula) and crystal structure.

3 Mineral Properties Color least reliable - do not use alone Color depends on the presence of certain ions, such as iron, chromium, cobalt Luster How the surface. Metallic vs. Non-metallic Streak Color of a mineral in. Cleavage The tendency of mineral s to break along planes of. Weaknesses within the structure allow the mineral to break along specific planes. This is called cleaving. Fracture. Hardness - A mineral s resistance to scratching & abrasion. Based on Moh s Hardness Scale (Table 3.3) Things that affect hardness 1. Atomic structure of the mineral 2. Type of chemical bonds which hold the mineral together 3. The types of atoms that form the mineral Specific Gravity (SG) Ratio of weight to an equal volume of water. Basically, how heavy it feels relative to other minerals. Things that affect density Atomic weight of the atoms Crystal structure Crystal Habit Characteristic shape as it grows. Ex. Quartz (6 sided), Garnet (12 sided) Atomic structure also affects how the mineral grows Special Properties of Select Minerals Smell and Taste Sulfur or Halite Fluorescence Some minerals glow under UV rays. Magnetism Magnetite Effervescence Calcite reacts with HCl (acid). Double Refraction Light is split into 2 rays = 2 images

4 Lecture Outline Friday - Monday Jan , 2018 Questions?? Lecture Quiz Friday January 27, 2017 Key Points for today Recognize that mineral are grouped by their crystal structure and composition What is the controversy associated with Asbestos? How are mineral deposits formed? What is a mineral deposit and why is it located where it is? What are the characteristic properties which make a mineral a gem? Where do diamonds come from and how do the make there way there? Mineral Groups Silicates Most abundant mineral group in the crust Dominates all three rock types Composed of Silicon and Oxygen= silica tetrahedron (SiO 4-4 ) Crystal structure Non-Silicates Carbonates, Oxides, Sulfides, Sulfates, Native Elements Why do some minerals have nice crystal form and others do not? If the mineral grows slowly and has space it will tend to form nice crystals, If many different minerals are growing at the same time and they are touching each other then they will grow together. Why are minerals important? We use minerals in our everyday life. Point to think on: Name a time in man s past where we did not rely on minerals or the materials made from minerals. How far back do we need to go in man s past? Are all minerals good for us? Asbestos, What s the deal? Asbestos is commercial definition for minerals that are flexible, chemically and thermally resistant and can be woven. Fiberous crystal form Previously used in building products (tiles, etc.) and insulation products. Heavy exposure to some types of asbestos has been linked to. Six minerals are considered to be commercial asbestos: Chrysotile (sheet silicate from the serpentine group) + four other double chain silicates from the serpentine group Crocidolite (double chain silicate from amphibole group) Asbestos, Do we need to spend $50,000,000,000 to $150,000,000,000 to get rid of it? Crocidolite

5 Forms sharp fibers (needles) that can puncture lungs Chrysotile Fibers dissolve more easily (not sharp) Has never been shown to cause lung related diseases. The only type of asbestos that is currently mined. The most commonly used type of asbestos in N. America. The key point is How do Minerals Form? Chemical reactions between elements. Crystallization. Where do minerals come from? 1. Lower the temperature of a liquid below its freezing point. Ex. Crystallization of a magma forming an igneous rock 2. - Liquids evaporate from a solution causing minerals to precipitate Lagoon is full of different ions and is restricted so water can not be replenished Liquids evaporate from a solution forming a supersaturated solution and results in precipitate NaCl - halite crystals form All Na is consumed. However, there are still other ions left with more evaporation Saturation of KCl (sylvite) and KCL crystals form and precipitate process continues until all water is evaporated Salt deposits are found worldwide found on almost all continents Examples where evaporates are currently forming:, Other mineral formed by evaporation are gypsum and anhydrite: Plaster of Paris and is used to make sheet rock for interior walls of houses. 3. Hydrothermal Fluids Hydrothermal fluids are created by the circulation of water through hot rock or near a magma chamber. The water is heated and is able to dissolve elements forming a weak acid solution. The hot acid solution is able to leach and pick up small amounts of gold and other metals and elements. The hot fluids rise and as they do they can precipitate the metals (by boiling, a change of temperature, change in acidity, or change in pressure). The result is that the gold and other metals are left behind and concentrated. Because the metals are concentrated to a sufficient level, it becomes economic for mining operations. Low grade concentration use open pit mining methods and high grade concentrations use much smaller underground tunnels for mining veins associated with faults and fractures in the rock. Mother Lode Au in California Au was leached from the surrounding rock by hydrothermal fluids associated with the Sierra Nevada Batholith. The gold was deposited in veins and with millions of years of weathering the gold was liberated

6 by erosion and washed into streams. Gold has a density of about 19gm/cc. Gold is very heavy and as a result it sinks to the bottom of the streams in low areas and becomes concentrated (placer deposit this is a very effective process). Placer gold was discovered in mid 1800 s at Sutters Mill starting the California gold rush. 4. Minerals formed by metamorphism: High heat and pressure allows different minerals to form while still in the solid state (nothing melts). Garnets and other metamorphic minerals form in this way. What makes a gem? Beauty - Brilliance based on hardness Diamonds Covalent bonds 10 on hardness scale Polymorph of carbon along with graphite Form in the mantle Most are believed to be very old (most about 3 billion years old). Brought to the surface through kimberlite pipes. Can be found as placer deposits. Uses: Gems, Cutting and Polishing Diamonds only exist on the surface because they were brought up fast, if they were allowed to equilibrate on the way to the surface the stable form of carbon would be graphite. Location of kimberlites (get from map) Are there gems more expensive than Diamond? In comparison to clear diamonds there are more expensive gems. Bixbite is a red beryl (same composition as Emerald but different color) and is very rare; maybe 1 or 2 localities in the world. One is in the Wah Wah Mountains in Utah. However, intensely colored are by far the most expensive.