Transcript 5.1 lecture
Chapter 5 Section 1 What is a mineral? Objectives 1.Define mineral. 2. Compare the two main groups of minerals. 3. Identify the six types of silicate crystalline structure. 4. Describe three common nonsilicate crystalline structures. How do you determine if a substance is a mineral? Yoav Yoav Levy Levy Classifying Minerals Four basic questions: Is the substance inorganic? • Magnetite is inorganic • Coal is organic and and contains iron and is made from oxygen. plants. Is it naturally occurring? • The mineral quartz occurs naturally in the earth. • Steel and brass are man-made. Is it a solid in crystalline form? • Diamond has a solid crystalline structure. • Petroleum and natural gas are naturally occurring but are not solids. Does it have a definite chemical composition? • The mineral fluorite is made of calcium and fluorine (CaF2) • Concrete is made up of several substances. Minerals: • must be inorganic • must be naturally occurring • must be a solid with an internal crystalline structure • must have a definite chemical makeup. There are over 3,000 known minerals • Many may be easily identified, although lab tests are needed to be conclusive. Yoav Levy Elements in the Earth’s Crust http://www.windows.ucar.edu/tour/link=/earth/geology/crust_elements.html&edu=high Even though there are 92 elements that are naturally found, only eight of them are common in the rocks that make up the Earth’s outer layer, the crust. Together, these 8 elements make up more than 98% of the crust. • The 8 most common elements in Earth’s crust (by mass): 46.6% Oxygen (O) 27.7% Silica (Si) 8.1% Aluminum (Al) 5.0% Iron (Fe) 3.6% Calcium (Ca) 2.8% Sodium (Na) 2.6% Potassium (K) 2.1% Magnesium (Mg) • The picture on the left shows where these elements are located within the periodic table. Together, the elements oxygen and silicon make up most of the Earth’s crust including silicate minerals such as quartz and feldspar. Rocks: • are solid materials that are made up of one or more minerals. Rock-forming minerals • Of the 3,000 minerals, fewer than 20 form most of the earth’s crust. Of these 20, only 10 are common, and these make up 90% of the earth’s crust All minerals can be classified into two main groups based on their chemical composition. • Silicates • Nonsilicates Silicate minerals contain atoms of silicon (Si) and oxygen (O) SiO2 Silicate minerals make up 96% of the earth’s crust. Quartz Feldspar (orthoclase) Feldspar (plagioclase) Silicates which are rich in iron and magnesium include: Hornblende Muscovite Olivine Biotite Nonsilicate Minerals • Make up only 4% of the earth’s crust • Six Major Groups Carbonates • Compounds that contain a carbonate group (CO3) Halides • Compounds that consist of chlorine or fluorine combined with sodium, potassium or calcium Native Elements • Elements uncombined with other elements Oxides Hematite Fe2O3 • Compounds that contain oxygen and an element other than silicon Sulfates • Compounds that contain a sulfate group (SO4) Sulfides • Compounds that consist of one or more elements combined with sulfur Crystalline Structure • a natural solid with a definite shape The conditions under which minerals are produced do not usually allow large single crystals to grow. Crystalline Structure of Silicate Minerals Silicon atom bonded to four atoms of oxygen in a pyramid arrangement • Silicon-oxygen tetrahedron Variations Ionic Silicates • Silicon-oxygen tetrahedra linked only by atoms of elements other than silicon and oxygen Single and Double Chained Silicates Single Chain Silicates • In single-chain silicates each tetrahedron is bonded to two others by shared oxygen atoms • Minerals made up of single chains are called pyroxenes Double Chain Silicates • In double-chain silicates, two single chains of tetrahedra bond to each other. • Minerals made up of double chains are called amphiboles Tetrahedral Sheets • Each tetrahedron shares three oxygen atoms with other tetrahedra. • The fourth oxygen atom bonds with an atom of K or Al, which joins one sheet to another. Examples of Tetrahedral Sheets • Biotite • Muscovite Network Silicates • Each tetrahedron is bonded to four neighboring tetrahedra • Network silicates tend to form very hard crystals. Examples of Network Silicates • Quartz • Feldspar Assignments • Section 5.1 Outline • Key Terms • Direct Reading