Transcript Geology
Geology Chapter 5 Minerals of Earth’s Crust 5.1 What is a Mineral? 5.1 What is a Mineral Objectives • Define mineral. • Compare the two main groups of minerals. • Identify the six types of silicate crystalline structures. • Describe three common nonsilicate crystalline structures. Introduction • A mineral is a natural, usually inorganic solid that has a characteristic chemical composition, an orderly internal structure, and a characteristic set of physical properties. Pyrite Sun - Illinois Characteristics of Minerals • An item must pass the “four questions” to be considered a mineral. – Is it inorganic? – Does it occur naturally? – Is it a crystalline solid? – Does it have a consistent chemical composition? • If the answer is yes to all the above questions, the item is a mineral. Characteristics of Minerals Kinds of Minerals • More than 3,000 kinds of minerals have been identified. • Fewer than 20 minerals are common – they are called the rock forming minerals. • Only 10 of the rock forming minerals make up 90% of the Earth’s crust. • Based on their chemical composition, minerals can be classified into one of two groups – silicate minerals and nonsilicate minerals. Kinds of Minerals • Silicate minerals contain a combination of silicon and oxygen, and they may contain one or more metals. • For example… – quartz is made only from silicon and oxygen – feldspar, the most common silicate contains potassium (potassium feldspar) or sodium or calcium – or both (plagioclase feldspar) – ferromagnesian minerals are rich in iron and magnesium – Feldspar and quartz alone make up 50% of the Earth’s crust Kinds of Minerals • Nonsilicate minerals do not contain silicon and oxygen and make up about 4% of the Earth’s crust. • Nonsilicate minerals are divided into six major categories by their chemical composition. – – – – – – Carbonates – contain carbonate group (CO3) Halides – Cl or F combined with Na, K, or Ca Native elements – pure elements Oxides – contain oxygen, but no silicon Sulfates – contain sulfate group (SO4) Sulfides – one or more elements combined with sulfur Crystalline Structure • A crystal is a solid whose atoms, ions, or molecules are arranged in a regular, repeating pattern. • The characteristic geometry of a crystal’s internal structure can be seen in large mineral crystals that grow uninhibited. • Minerals are commonly made up of masses of microscopic crystals. Beryl Crystal in Quartz - Brazil Crystalline Structure of Silicate Minerals • The silicon-oxygen tetrahedron is the basic unit of the structure of silicate minerals; a silicon ion chemically bonded to and surrounded by four oxygen ions. http://www.winona.edu/geology/MRW/mrwi mages/tetrahedron.jpg Crystalline Structure of Silicate Minerals • Silicon-oxygen tetrahedra combine in a variety of arrangements to form different silicate minerals. – Isolated tetrahedra – do not link with other silicon or oxygen atoms – Ring silicates – form rings by sharing oxygen atoms – Single-chain silicates – form a chain by sharing oxygen atoms – Double-chain silicates – form when two single chains of tetrahedra bond to each other – Sheet silicates – form when each tetrahedron shares three of it s oxygen atoms with other tetrahedra – Framework silicates – form when each tetrahedron is bonded to four other tetrahedra *See Figure 3 pg. 107. Six Kinds of Silicate Mineral Arrangements Six Kinds of Silicate Mineral Arrangements Six Kinds of Silicate Mineral Arrangements The Crystalline Structure of Nonsilicate Minerals • Nonsilicate minerals display a variety of crystal structures including cubes, hexagonal prisms, and irregular masses. • The structure of the nonsilicate mineral determines the characteristics of that mineral. Dogtooth Calcite – Unknown Origin The Crystalline Structure of Nonsilicate Minerals • In native elements, for example, atoms are packed together as close as possible (closest packing). • Closest packing results in the higher densities of metals. • Each metal atom may be surrounded by 8 to 12 other metal atoms which are as close to each other as the charges of the atomic nuclei will allow. Native Copper - Michigan