Minerals - Minerals Chapter 3 Minerals Chapter 3 What are...

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Unformatted text preview: Minerals Chapter 3 Minerals Chapter 3 What are minerals? Minerals are Solid Naturally occurring Limited chemical composition can have the same chemical composition, but be a different mineral.. crystal lattice-defined by the arrangement of the atoms and the bonds. Crystal System Lattices Crystal System rhombohedral Lattices triclinic monoclinic tetragonal orthorhombic cubic hexagonal 1 Minerals Chapter 3 regular atomic arrangement crystals What are they made of? Minerals are made of atoms different elements positive and negative teams joined in the crystal lattice How do atoms bond together to form crystals? First note atoms balance between protons and electrons Note shells of electrons First - 2 Second - 8 Third - 14 Unfilled shells means they "want to date" with another element to share electrons http://en.wikipedia.org/wiki/Electron_shells http://en.wikipedia.org/wiki/Crystals 2 Minerals Chapter 3 Also look up graphite & diamonds and the difference in bonds Atoms with unfilled shells Look for partners positive seek negative What kind of bonds for between atoms? Major kinds Ionic Covalent Minor kinds metallic bonding (gold) van der waals bond (graphite) How do ionic bonds form? Electron transfer from positive ion (cation) to negative ion (anion) these are WEAK bonds common in salts minerals often dissolve in water NaCl... look up... halite How do covalent bonds form? they share electrons the more shared electrons, the stronger the bond but bonds form in different planes and/or 3-D patterns this results in mineral properties Either way, a crystal forms! Positive and negative units regular arrangements strong and weak planes or three dimensions of bonds What mineral properties reveal their composition? find some pictures of green igneous rocks and pink igneous rocks... dark and light igneous rocks Table 3.2 in book color not the most reliable... but most obvious can be tricky but can help Igneous dark group light group hardness if minerals can scratch glass it is harder than a 6 Mohs Scale: Common references Knife blade Mechanical pencil steel steel file glass penny fingernail cleavage 3 Minerals Chapter 3 look up learn spelling defined by planes of weak bonds extreme is mica can have it in 1, 2, 3 directions some cleavage patterns are not in 90 degrees planes of weak bonds relative to planes of strong bonds not all minerals have this some have planes that have vary strong bonds (IE diamonds, window glass) very useful in some situations pyroxenes and amphiboles difference in degrees of cleavage can tell where the cleavage is by where the sunlight reflects can use hand lens for small crystals in rocks crystal habit what the crystal looks like if allowed to grow by itself without any changes Natural, exterior shape of the crystals some classes: prismatic cubic polyhedral terminated (hexagonal where all the facets converge) platy very uncommon because they have to grow in a completely unconfined space most crystals grow together, confined euhedral crystals must be unconfined (in voids, like geodes)... have points most crystals are anhedral because most grow in confined space... so these have no points can have both euhedral and anhedral in the same rock if there was one rock that was euhedral and then another mineral crystalized later to become anhedral luster the way the light hits it specific gravity g/cm3 others IE taste how are minerals classified? picture 3.10 page 79 SiO4-4 Groups based on negative ion cations and anions join in crystaldom note: Large negative ions, small positive ions one or more cations bond with anion or radical Free radicals tightly bonded compounds behave like ions in many crystals we'll focus on the SILICA TETRAHEDRON building block of the SILICATE MINERALS 4 Minerals Chapter 3 What are silicate minerals? 95% of the earth's surface is made of silicate minerals minerals containing the SiO4 tetrahedron form almost all of the igneous and metamorphic minerals Silica tetrahedron note interlocking covalent bonds "action" will be at the oxygens What are silicate minerals? crustal elemental composition Note mantle composition has less silica and aluminum... more iron and magnesium How are silicate minerals classified? figure 3-13 in book Tetrahedral arrangements isolated--olivine single chain--pyroxenes double chain--amphiboles sheets--mica, clay 3-D networks--quartz, feldspars important silicate minerals Ferromagnesian Silicates Iron (Fe) Magnesium (Mg) or both Pyroxenes and Amphiboles... Note Cleavage angles GRANITE! Quartz Potassium Feldspars Mica other accessories Feldspars How do silicate minerals form together in rocks? Igneous Almost all are silicate Metamorphic Almost all are silicate Sedimentary Quite a few are silicate 5 ...
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This note was uploaded on 08/18/2008 for the course GEOL 1610 taught by Professor Byers during the Fall '08 term at North Texas.

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