GEOL 1425 1st EditionExam # 2 Study Guide Lectures: 6 - 12Earth Minerals: Minerals and Rocks (Chapter 3) What you need to know about earth minerals for the test: o What constitutes a mineral? –building blocks of rocks, a naturally occurring, solid crystalline substance, usually inorganic, with a specific chemical composition. They’re homogenous. To qualify as a mineral, a substance must be found in nature. o Be familiar with the atomic structure of matter (nucleons, electrons, atomic number, atomic mass, isotopes). Nucleus consists of protons (+1 charge) and neutrons (neutral/0 charge). The electrons surround the nucleus and its mass is so small it is taken to be 0 (-1 charge).  Atomic number= the number of protons in the nucleus of an atom Atomic mass= the sum of the masses of its protons and its neutrons Isotopes= atoms of the same element with different numbers of neutronso Know the differences between covalent and ionic bonding. Be familiar with their processes.  Covalent bonding= electron sharing! This is when elements do not readilygain or lose electrons, they share them instead. These are stronger bonds.  Ionic bonding= electron transfer. These are weaker and simplest form of bonds. Form by electrostatic attraction between ions of opposite charge when electrons are transferred. The strength of ionic bonds decreases as the distance between ions increases, and it increases the electrical charges of the ions increase. About 90% of all minerals are ionic. o Know the rock forming minerals- the silicates and their structures Contain oxygen and silicon. Basic building block of silicates is a silicate ion,which is a tetrahedron shape. Has a negative charge, so often bonds to cations (+ charge) to form minerals.  The most abundant minerals in Earth’s crust, are composed of O and Si, the 2 most abundant elements in the crust, mostly in combination with the cations of other elements.  4 types of silicate minerals: isolated silica tertahedra (linked by the bonding of each oxygen ion of the tetrahedron to a cation), single-chain linkages (formed by the sharing of oxygen ions), double-chain linkages (two single chains may combine to form double chains linked by shared oxygen atoms), sheet linkages (each tetrahedron shared 3 of its oxygenions with adjacent tetrahedral to build stacked sheets), and frameworks (form as each tetrahedron shared all its oxygen ions with other tetrahedral). o Know the rock forming minerals- the non-silicate mineral types (carbonates, oxides, sulfides, etc.) Carbonates contain carbon and oxygen. Groups are arranged in sheets Oxides contain oxygen and metallic cations. Most are ionically bonded and their structures vary with the size of the metallic cation Sulfides contain S and metallic cations. Most look like metals and almost all are opaque. Sulfates contain SO4 and metallic cations. Tetrahedron made up of a central sulfur atom surrounded by 4 oxygen ions. Halides contain Cl, F, I, or Br. Hydroxides contain OH Native elements are masses of all the same element metallically bonded. o What are the physical properties of minerals? Hardness= the measure of ease with which the surface of a mineral can be scratched. Mohs scale of hardness identified the most extreme softness of a mineral as 1 (talc, the softest) and the most extreme hardness of a mineral as 10 (diamond, the hardest). Cleavage= the tendency of a crystal to split along planar surfaces. Also used to describe the geometric pattern produced by such breakage. Strong (covalent) bonds produce poor cleavage and weak (ionic) bonds produce good cleavage.  Fracture= the tendency of a crystal to break along irregular surfaces otherthan cleavage planes. All minerals show fracture. Conchoidal- showing smooth and curved surfaces like broken glass, OR fibrous/splintery- like split wood.  Luster= the way the surface of a mineral reflects light. Metallic, vitreous (bright like glass), resinous, greasy, pearly, silky, adamantine (the brilliant luster of diamond) Color= imparted by light, either transmitted through or reflected by crystals or irregular masses of the mineral. Color is distinctive in minerals,but is NOT the most reliable clue to its identity.  Streak= refers to the color of the fine deposit of mineral powder left on an abrasive surface when a mineral is scraped across it. Streak is a little more reliable an identifier than color alone.  Density= difference is weight. Standard measure of density is specific gravity—the weight of a mineral divided by the weight of an equal volume of pure water at 4 degrees C. Crystal habit= the shape in which individual crystals grow. Fibrous crystalstake shape as multiple long narrow fibers (essentially like long needles), and asbestos is a group of silicate minerals with a more/less fibrous habit that allows the crystals to become embedded in the lungs if they are inhaled. Igneous Rocks (chapter 4)They form by crystallization of magma. Intrusive igneous rocks form when magma intrudes into un-melted rock masses deep in Earth’s crust and have large interlocking crystals. Extrusive igneous rocks form from magmas that erupt at Earth’s surface as lave and cool rapidly and are glassy.  What you need to know for the test about Igneous rocks:o Details of Gabbro’s, porphyrys, and phenocrysts Gabbro: an intrusive, mafic igneous rock. Rapid cooling at earth’s surface produces the fine-grained texture or glassy appearance of extrusive igneous rocks such as gabbro. Mafic minerals are the lowest in silica and crystalize at higher temperatures than felsic minerals.  Porphyry: an igneous rock that has a mixed texture in which large crystals “float” in a predominantly fine-grained matrix.  Phenocrysts: the large crystals in porphyry that form in magma while it is still below Earth’s surface. Before the crystals can grow, a volcanic eruption brings the magma to the surface where it cools quickly to a finely crystalline mass.o What is the effect of water on rock melting? –the melting points of various silicates decrease in proportion to the amount of water dissolved in the molten silicate. Water content is a significant factor in determining melting temperatures of mixtures of sedimentary and other rocks. Sedimentary rocks contain an especially large volume of water in their pore spaces (more than igneous or metamorphic). Adding water to a