Earth Materials: Minerals. Mineral Properties. Mineral Properties. Some optical properties. Three general categories:

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1 1 2 Earth Materials: Minerals What is a mineral? Properties/characteristics of different types of minerals Mineral structures and bonding Major categories of minerals Importance and uses of minerals What is a mineral? Requirements for something to be considered a mineral: - naturally occurring - inorganic - solid - crystalline - contains specific composition of elements Three general categories: Optical Physical Chemical 3 Some optical properties Color Streak Luster Double refraction Fluorescence Transmission of light (transparent, translucent, or opaque) 4 5 Streak Example: hematite Fig Minerals of various colors 1

2 Metallic luster: gold and pyrite 7 Double refraction in a transparent piece of calcite 8 Non-metallic luster: feldspar, mica, olivine, and quartz 9 10 Some physical properties Hardness Density Crystal shape How it breaks: cleavage and fracture 11 How a mineral breaks: 12 Fracture - when a mineral breaks along irregular surfaces - any mineral may exhibit fracture - some particular types of fracture have names: irregular (rough with no particular pattern), conchoidal (with smooth, curved surfaces like glass), fibrous or splintery (similar to broken wood), etc. Crystal of galena (left) (lead sulfide) Crystal of quartz (right) (silicon dioxide) Galena, which contains lead, is much more dense than quartz. The two minerals also have different crystal shapes. Fig 2.10 Cleavage - when a mineral breaks along flat, planar surfaces - some minerals have cleavage & others do not - key observations: - number of different cleavage directions - angle between cleavage directions 2

3 13 14 Conchoidal fracture in obsidian Fig 4.3 Cleavage of mica into thin sheets Fig Cleavage angles Fig Cleavage in calcite Fig 2.24 Chemical properties Acid test Salty taste Many other chemical tests 17 Some other properties Habit Magnetism Absorbs water Smell 18 Acid test for calcite Fig

4 barite rosettes (barium sulfate) needles of stibnite (antimony sulfide) 19 Fibers of chrysotile (one type of asbestos) 20 Some unusual crystal Habits Chapter 2 Geology 2 nd ed. Chernicoff botryoidal malachite (green) with azurite (blue) (hydrous copper carbonates) stellate pyrite (iron sulfide) In-class exercise Relationship to: Working in groups, examine and describe the properties of each mineral sample provided atomic composition atomic structure and bonding Chemical bonds - how multiple atoms are held together ionic - attraction between ions of opposite electrical charge - example: Na+ and Cl- ions combine to form halite - the most common type of bonding in minerals covalent - sharing of electrons between atoms - the strongest type of chemical bond - metals have a particular type of covalent bond called a metallic bond other types of bonding e.g. van der Waals bonds, a very weak type of bonding 23 Graphite and Diamond Both are composed of carbon but have very different properties. Fig

5 Carbon atom Fig Structures of graphite (left) and diamond (right) Geology 2 nd ed. - Chernicoff 27 Structure of halite (sodium chloride - salt) Fig 2.16 Regular arrangement of atoms in galena (left) Cube-shaped crystals (below) 28 Ionic bonds hold together Cl -1 and Na +1 The structure of galena is essentially the same as in halite. Therefore, both grow and break to form cubes. Their color and luster are different, however, because they have different compositions (and bonding). Fig Some major groups of minerals 30 Silicates e.g. quartz, feldspar, mica, olivine Non-silicates: Carbonates Oxides Sulfides Sulfates Native elements Halides e.g. calcite e.g. magnetite, hematite e.g. pyrite, galena e.g. gypsum e.g. native gold, copper e.g. halite 5

6 31 32 individual tetrahedra single double sheets chains chains Silicon-oxygen tetrahedron Fig 2.16 Types of silicate mineral structures Figs 2.17 and D frameworks Mica is built from numerous sheets. 33 Importance of Minerals 34 This explains the single direction of cleavage found in micas. Muscovite Mica Almost all rocks are made of minerals! Aesthetic value Gemstones museum specimens Natural resource value source of metals needed for electronics manufacture, cars, airplanes, etc. raw materials for making window glass, plaster/sheetrock, etc. Geology 2 nd ed. - Chernicoff Minerals as Constituents of Rocks 35 Aesthetic value 36 Native gold Smithsonian A large cut diamond Smithsonian Minerals in Granite Alkali Feldspar (Orthoclase) Amphibole (Hornblende) Quartz Plagioclase feldspar, Muscovite mica, and Biotite mica also may be found in some granites 6

7 37 38 A great deal of effort goes into obtaining key mineral resources Iron ores magnetite, iron+oxygen (left) siderite iron+carbon+oxygen (top) Fig pyrite iron+sulfur (right) hematite iron+oxygen (bottom) Open pit copper mine south of Tucson, Arizona Fig U.S. reliance on imported mineral resources 39 U.S. reliance on imported mineral resources 40 Fig Fig Some Online Resources 41 Mineral resources info. from the USGS WebMineral Minerals Database MinDat Minerals Database Smithsonian Gem & Mineral Collection Smithsonian Department of Mineral Sciences More rock and mineral links (some with lesson plans) (Digital Library for Earth System Education) 7