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Introduction to Minerals A little bit about Earth •As far as we know, no other planet in the solar system has the unique combination of having all three forms of water. •Earth has a surface that is covered with liquid water, has water vapor in the atmosphere, and frozen water on the land. •Earth also had solid material making up the surface of the planet. This is going to be our next unit: Rocks, Minerals and the interaction of Earth with water. Earth’s Molten Stage • During the early formation of the Earth, it was molten • During this stage the denser elements, such as iron and nickel, sank to the deeper interior of the Earth. • As the Earth cooled, a thin layer of less dense materials on the surface formed the crust. Earth’s Crust Chemical Composition • 8 major elements make up 98.6% of the crust-for simplicity you need to know two of them, Oxygen and Silicon • These 8 elements make up the solid materials of the Earth’s crust and can form minerals and rocks • A mineral is 1. 2. 3. 4. 5. a solid, inorganic naturally occurring material that has both a known chemical composition and a crystalline structure that is unique to that mineral • A rock is a solid, combination of one or more minerals • THEREFORE: minerals make up rocks Common Materials of Earth Details on Minerals 1. Crystal Structures a. A crystal is a structural unit (pattern) that is repeated in three dimensions. 2. Density – ratio of the mass of a mineral to its volume. a.Specific gravity – ratio of mineral density to the density of water b. Density Depends on: Kind of atoms which make up the mineral How the atoms are arranged in the crystal This is the basic structural unit of a crystal of sodium chloride, the mineral halite. The structural unit for a crystal of table salt, sodium chloride, is cubic, as you can see in the individual grains. These quartz crystals are hexagonal prisms. Details on Minerals 3. Color A visual measure. Not very useful for identification as color of minerals vary. 4. Streak This is the color of the mineral when it is finely powdered. We measure this by rubbing it across a piece of ceramic tile, leaving a fine powder of the mineral on the tile. 5. Hardness Resistance of the material to being scratched. Measured using the Mohs hardness scale, which compares the hardness of the mineral to 10 reference minerals. (A)Gypsum, with a hardness of 2, is easily scratched by a fingernail. (B) Quartz, with a hardness of 7, is so hard that even a metal file will not scratch it. Details on Minerals 6. Cleavage The tendency of mineral to break along smooth, predicable planes . Depends upon areas of weakness in the crystal structure. A. Fracture The broken surface is irregular and not in a flat plane. Resource: http://academic.brooklyn.cuny.edu/geology/grocha/mineral/cleavage. html Details on Minerals 7. Luster Surface sheen (the look). Could be: Metallic – like metal WaxyPearly – like pearl (shiny, but not see-through) Vitreous – glasslike Earthy- How Minerals Form In general, minerals can form in two ways: through cooling of melted materials, and through materials dissolved in water. Minerals can form as hot magma cools deep inside the crust, or as lava hardens on the surface. When water evaporates it leaves behind residue that forms mineral crystals. Mineral-Forming Processes-Cooling Magma: Molten material under the Earth’s surface from which minerals are formed VS Lava: Magma that is forced to the surface of Earth Influences on the mineral forming process: 1. Temperature 2. Pressure 3. Time 4. Availability and concentration of ions that are in solution • Bowen’s Reaction Series • Arranges the minerals by what temperature they form at. •The size of these crystals (the minerals) depends on several factors. •The rate at which magma cools, the amount of gas magma contains, and the chemical composition of magma all affect crystal size. Minerals at the top of the series (olivine, augite, and calciumrich plagioclase) crystallize at higher temperatures, leaving the magma enriched in silica. Later, the leftover magma cools and less dense minerals (orthoclase feldspar, quartz, and white mica) crystallize. So the temperature of the magma determines the minerals it will turn into. •Slow cooling leads to the formation of minerals with large crystals. •If the crystals remain undisturbed while cooling deep below the surface, they grow according to a regular pattern. •On the surface, lava loses heat energy much faster than magma that hardens deep below ground. •With rapid cooling, there is no time for magma to form large crystals. Intro to Minerals Movie https://www.youtube.com/watch?v=8a7p1NFn64s