Earth image Minerals

Dr. Pamela Gore
Georgia Perimeter College

Objectives

  1. Identify minerals, which are the building blocks of rocks
  2. Distinguish between rocks and minerals.
  3. Describe the 5 characteristics of minerals.
  4. Describe ways in which minerals form or crystallize.
  5. Distinguish the physical properties that are useful in identifying minerals.
  6. Distinguish the chemical characteristics that are useful in identifying minerals.
  7. List the eight most common elements of the earth's crust
  8. Briefly describe the silicon-oxygen tetrahedron.
  9. List and distinguish among the common silicate minerals.
  10. List the benefits or economic uses of some common minerals.
  11. Describe the chemical classification of minerals.
This section addresses, in whole or in part, the following Georgia GPS standard(s):
  • S6E5b. Classify rocks by their process of formation.
  • S3E1a. Explain the difference between rocks and minerals.
  • S3E1b. Recognize the physical attributes of rocks and minerals using observation (shape, color, texture), measurements, and simple tests (hardness)

This section addresses, in whole or in part, the following Benchmarks for Scientific Literacy:
  • The earth is mostly rock. Three-fourths of its surface is covered by a relatively thin layer of water (some of it frozen), and the entire planet is surrounded by a relatively thin blanket of air. It is the only body in the solar system that appears able to support life. The other planets have compositions and conditions very different from the earth's.
  • Some minerals are very rare and some exist in great quantities, but-for practical purposes-the ability to recover them is just as important as their abundance. As minerals are depleted, obtaining them becomes more difficult. Recycling and the development of substitutes can reduce the rate of depletion but may also be costly.
  • Rock is composed of different combinations of minerals. Smaller rocks come from the breakage and weathering of bedrock and larger rocks. Soil is made partly from weathered rock, partly from plant remains-and also contains many living organisms.

This section addresses, in whole or in part, the following National Science Education Standards:
  • Some changes in the solid earth can be described as the "rock cycle." Old rocks at the earth's surface weather, forming sediments that are buried, then compacted, heated, and often recrystallized into new rock. Eventually, those new rocks may be brought to the surface by the forces that drive plate motions, and the rock cycle continues.
  • Soil consists of weathered rocks and decomposed organic material from dead plants, animals, and bacteria. Soils are often found in layers, with each having a different chemical composition and texture.
  • A substance has characteristic properties, such as density, a boiling point, and solubility, all of which are independent of the amount of the sample. A mixture of substances often can be separated into the original substances using one or more of the characteristic properties.

Minerals

Definitions

Mineral
  1. Naturally occurring
  2. Inorganic
  3. Solid
  4. Definite chemical composition
  5. Orderly internal crystal structure

What are some examples of some mineral names?

  1. Feldspar is the most abundant mineral in the Earth's crust. There are several types of feldspar including:
    1. Orthoclase feldspar
    2. Microcline feldspar
    3. Plagioclase feldspar (has striations - tiny parallel hairline grooves)
  2. Quartz is the second most abundant mineral in the Earth's crust
  3. Other common rock-forming minerals include:
    1. Muscovite mica
    2. Biotite mica
    3. Hornblende (part of the amphibole group of minerals)
    4. Augite (part of the pyroxene group of minerals)
    5. Olivine
    6. Calcite is common in some sedimentary rocks
  4. Other minerals have economic value or may have industrial uses:
    1. Diamond
    2. Native gold
    3. Native copper
    4. Barite (mined in Georgia)
    5. Kaolinite (mined in Georgia)
    6. Talc
    7. Gypsum
    8. Corundum (ruby and sapphire)
    9. Pyrite
    10. Native sulfur
    11. Magnetite
Can you find out what these minerals are each used for?

Rock

A rock is an aggregate of one or more minerals

What are some examples of some rock names?

  1. Granite
  2. Basalt
  3. Pumice
  4. Sandstone
  5. Limestone
  6. Chalk
  7. Shale
  8. Marble
  9. Schist
  10. Slate

Polymorphs

 Two minerals with the same chemical composition, but a different crystal structure.

Examples?

Return to Outline

Physical Properties of Minerals

  1. Color

    2. not always diagnostic (feldspar, quartz, fluorite come in many colors)

    Feldspar can be green, pink white, gray, etc.

  2. Luster

    3. metallic
    non-metallic
          glassy or vitreous, dull, pearly,
          resinous, waxy, adamantine, silky

  3. Streak

    4. unglazed porcelain plate
    note color, odor if any

    Both of these samples are hematite; both have a reddish-brown streak

  4. Hardness

    5. scale of 1 to 10 (Mohs Scale)

    1. Talc
    2. Gypsum
      ________ fingernail
    3. Calcite
      ________ penny (copper)
    4. Fluorite
      _________ nail
    5. Apatite
      _________ glass
    6. Orthoclase feldspar (K feldspar)
    7. Quartz
    8. Topaz
    9. Corundum
    10. Diamond

  5. Cleavage

    6. Breakage along planes
    Related to crystal structure

    1 direction

    (muscovite, biotite)

    Muscovite (left) Biotite (right)

    2 directions at 90°

    (feldspar, pyroxene)


    Pyroxene

    2 directions not at 90°

    (amphibole at 60° and 120°)

    3 directions at 90° (cubic)

    (halite, galena)


    Halite

    3 directions not at 90° (rhombohedral)

    (calcite, dolomite)


    Cleavage fragments of calcite

    4 directions (octahedral)

    (fluorite)

    Cleavage fragments of fluorite

    6 directions

    (sphalerite)

  6. Fracture

    7. irregular breakage (no cleavage)
    breakage not along smooth planes

    Conchoidal fracture

    smooth curved fracture surfaces
    occurs in quartz, chert, obsidian, glass


    Rose quartz lacks cleavage; it has conchoidal fracture


    Conchoidal fracture in the igneous rock, obsidian

  7. Crystal form

    8. Some minerals that may or may not have cleavage GROW (not break) into crystals with flat sides.

    Examples
    quartz
    pyrite

    Quartz crystals

  8. Density

    9. Density = mass divided by volume

  9. Specific gravity

    10. (similar to density)

    Weight of a mineral divided by weight of an equal volume of water.

  10. Magnetism

    11. Can be picked up by a magnet or may be a natural magnet

  11. Reaction to hydrochloric acid (HCl)

    12. Calcite effervesces in acid

    CaCO3 + 2HCl = CO2 + H2O + CaCl2

    Dolomite CaMg(CO3)2
    Must be scratched and powdered to fizz

  12. Taste

    13. halite, sylvite

  13. Fluorescence

    14. Some minerals glow in the dark under a black light (U.V. light)

    Due to excitation of electrons

  14. Double refraction

    15. Light passing through the mineral is split into two rays. Causes an optical "doubling" effect.

    Calcite

    Calcite has the optical property of double refraction. In the photos above, the same sample of calcite is used. It is rotated over a thin dark line. Examine how the appearance of he line changes inthe different orientations of calcite.

    Chemical classification of minerals

    1. Native elements (metal)
      native gold (Au), native copper (Cu), native sulfur (S), native silver (Ag), graphite (C), diamond (C)
    2. Sulfides (metal + S)
      pyrite (FeS2), galena (PbS), sphalerite (ZnS)
    3. Sulfates (metal + SO4)
      gypsum (CaSO4 · 2H2O), anhydrite (CaSO4), barite (BaSO4)
    4. Oxides (metal + O)
      water ice (H2O), hematite (Fe2O3), magnetite (Fe3O4), corundum (Al2O3)
    5. Halides (metal + Cl or F halogens)
      halite (NaCl), fluorite (CaF2)
    6. Hydroxides (metal + OH)
      limonite (iron hydroxide), bauxite (aluminum hydroxide)
    7. Carbonates (metal + CO3)
      calcite (CaCO3), dolomite (CaMg(CO3)2)
    8. Phosphates (metal + PO4)
      apatite
    9. Other - borates, urananates
    10. Silicates (metal + Si and O)
      quartz (SiO2),
      potassium feldspar (KAlSi3O8),
      Ca Plagioclase feldspar (CaAl2Si2O8),
      Na Plagioclase feldspar (NaAlSi3O8)
    Return to Outline

    Silicate Structures

     Based on silicate tetrahedron
    4 oxygen atoms and 1 silicon atom

    1. Single tetrahedra
      olivine

    2. Single chains
      pyroxene

    3. Double chains
      amphibole

    4. Sheets
      muscovite
      biotite

    5. Frameworks
      quartz
      feldspar
      potassium feldspars (orthoclase and microcline)
      plagioclase feldspars

    The eight most common elements in the Earth's crust:

    Element Approx. Weight %
    Oxygen (O)46.6
    Silicon (Si)27.7
    Aluminum (Al)8.1
    Iron (Fe)5.0
    Calcium (Ca)3.6
    Sodium (Na)2.8
    Potassium (K)2,6
    Magnesium (Mg)2.1
    All others1.7

    The State Mineral of Georgia

    The State Mineral of Georgia is staurolite.
    Staurolite is a silicate mineral that forms in some metamorphic rocks. Staurolite can be found near Blue Ridge, in Fannin County, GA and in a number of other areas.

    Staurolite is a brownish mineral that is commonly found as small rectangular crystals about the size of a cough drop or a little larger than a piece of Pez. Staurolite may be found as a single rectangular crystal or it may be found "twinned" where two rectangular crystals are intergrown with one another to form a cross. Twinned staurolite crystals are sometimes referred to as "fairy crosses". The cross is not always at 90o. More commonly, the two crystals are twinned at a different angle, forming an X-like shape (called a St. Andrews cross).

    For pictures of staurolite crystals:
    click here or here. There are some nice pictures here of staurolite crosses made into jewelry.
    Learn about the legends and myths of the fairy crosses here.

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    Page created by Pamela J.W. Gore
    Georgia Perimeter College,
    Clarkston, GA

    Page created May 7, 2005
    Image links and email updated June 12, 2008