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Chapter 2

GLG110 Textbook Notes Exploring Geology 2nd Ed Chapter 2

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University of Toronto St. George
Earth Sciences

Chapter 2: Minerals  Geologists study minterals both to understand the formation of rocks and to locate and extract resources that you use every day.  Many rocks look uniform from a distance, but upon closer examination clearly consists of smaller components called minerals. Luster – The property that describes how mineral surfaces reflect light. Crystal Faces – Distinct faces that minerals have which are smooth, flat surfaces with regular geometric outlines. Specific Gravity – The weight of a material in air divided by the weight of an equivalent volume of water at 4 degrees celcius. Hardness – A measure of the resistance of a mineral surface to scratching. - Measured using the Mohs Hardness Scale. It is a relative scale with values b/w 1 - 10 Cleavage – Describes the flat, smooth planes along which some minerals break and the shape of the resulting fragments. - Non-uniform breakage is fracture, rather than cleavage.  Color is not always a reliable property for identifying a mineral because many minerals can have the same color. Color Streak – The color of the residue produced by scratching a mineral on a nonglazed porcelain plate. - A mineral may vary in color, but its streak color is always the same. What are the Properties of Minerals?  Minerals have observed or easily measured physical properties, some of which are more diagnostic than others for recognizing a specific mineral.  The principal physical properties used to describe the minerals are color, luster, streak, hardness, cleavage, specific gravity, and external crystal form. What are Minerals Composed of?  Minerals are chemical compounds consisting of combinations of atoms of one or more elements.  Each mineral has a definitive, but possibly slight varying, chemical composition. How do we know…the Atomic Structure of Minerals?  Geologists use TEM microscropes to visualize arrangements of atoms inside minerals.  TEM images, made by firing electrons into a mineral sample, show the orderly internal arrangement of atoms unique to each mineral.  Each mineral consists of atoms of particular elements arranged in an orderly pattern.  Distribution of electrons around atomic nuclei determines how atoms bond. Ions – Positively or negatively charged particles. Ionic Bonds – Formed by the attraction of negative & positive ions in order to balance their charges. Covalent Bonds – Two or more atoms mutually share electrons to fill the outer electron layer. Metallic Bonds – Electrons roam freely around a number of different atoms, typically of the same element. This explains why metallic substances can conduct electricity. Van der Waals Force – Weak attraction of neutrally charged particles.  Minerals solubility in water depends on the strength of the ionic bonds. o Adding acid to water can further enhance solubility. Polymorph – Minerals with identical chemical composition but with different arrangements of atoms. How do Elements Combine to Make Minerals?  Minerals are atoms of elements combined by ionic, covalent, and less common metallic bonds and weak van der waals forces.  Ionic bonds are weaker than covalent bonds, where atoms share electrons.  The neutral, but lopsided, water molecule has a weak positive charge at one end and a negative charge at the other. These charges pull apart some weakly bonded ions, causing some minerals to dissolve in water.  Many mineral
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