Earth Materials: Minerals. Importance of Minerals. Introduction to Scientific Classification

Transcription

1 Earth Materials: Minerals Intro. to Scientific Classification 1 Introduction to Scientific Classification Assigning objects, processes, etc. into groups or categories 2 What is a mineral? Importance and uses of minerals Describing and identifying minerals Mineral properties Why these properties? - Mineral structures, bonding, and composition Major categories of minerals Based on composition and structure Minerals and Mineral Resources information (updated often by D. Kuehn) Geologic materials like fossils, minerals, rocks, faults, and volcanoes have been classified into categories What is a mineral? - solid (excludes liquids and gases) - crystalline (three dimensional ordered arrangement of atoms or molecules) - specific composition (a single element or a compound that at least comes close to a specific chemical formula) - naturally-occurring (not exclusively made by people on purpose) - single-phase (made up of one kind of material; not a mixture i.e. to distinguish minerals from rocks) 3 Importance of Minerals Almost all rocks are made of minerals! Aesthetic value Natural resource value 4 usually not of biological origin / inorganic (somewhat artificial distinction here) Examples to test: Ice (e.g. in snow or a glacier) Obsidian Minerals as Constituents of Rocks 5 Aesthetic value 6 Native gold Smithsonian A large cut diamond Smithsonian Minerals in Granite 1

2 Natural Resource Value 7 Importance of Minerals 8 Natural resource value Our society can t function without minerals! Open pit copper mine south of Tucson, Arizona Mineral Information Institute - Lifetime consumption - Per-capita minerals use - Importance of mining - Fact sheets, etc. Fig Three general categories: Some optical properties Optical Physical Chemical Color Streak Luster Double refraction Fluorescence Transmission of light (transparent, translucent, or opaque) Streak Example: hematite Fig 2.26 Minerals of various colors 2

3 Metallic luster: gold and pyrite 13 Double refraction in a transparent piece of calcite 14 Non-metallic luster: feldspar, mica, olivine, and quartz Some physical properties Hardness Density Crystal shape How it breaks: cleavage and fracture 17 How a mineral breaks: 18 Fracture Cleavage Crystal of galena (left) (lead sulfide) Crystal of quartz (right) (silicon dioxide) These minerals differ in color, luster, light transmission, crystal form, hardness, cleavage, and streak. - key observations for cleavage: - number of directions - angles between them Fig

4 19 20 Conchoidal fracture in obsidian Fig 4.3 Cleavage of mica into thin sheets Fig Chemical properties Acid test Salty taste Many other chemical tests 22 Cleavage in calcite Fig 2.24 Fig barite rosettes (barium sulfate) needles of stibnite (antimony sulfide) 24 Some other properties Habit Some unusual crystal Habits Magnetism Geology 2 nd ed. Chernicoff Absorbs water Smell botryoidal malachite (green) with azurite (blue) (hydrous copper carbonates) stellate pyrite (iron sulfide) 4

5 25 26 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 covalent metallic other types of bonding Graphite and Diamond Both are composed of carbon but have very different properties. Fig 2.15 Carbon atom Fig Structures of graphite (left) and diamond (right) Geology 2 nd ed. - Chernicoff 5

6 31 Structure of halite (sodium chloride - salt) Fig 2.16 Regular arrangement of atoms in galena (left) Cube-shaped crystals (below) 32 Ionic bonds hold together Cl -1 and Na +1-1 The structure of galena is essentially the same as in halite. Therefore, both +1 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 34 Silicates e.g. quartz, feldspar, mica, olivine (categorized by type of structure) 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 individual tetrahedra single chains double chains sheets Silicon-oxygen tetrahedron Fig 2.16 Types of silicate mineral structures Figs 2.17 and D frameworks 6

7 37 Some Online Resources 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