Properties of Rocks and Minerals

Guide to Rocks, Diamonds, and Minerals (Thanks, Stephanie)

Guide to Diamonds, Rocks and Minerals (Thanks, Courtney and Kids).

  1. Most of the material that makes up soil comes from rocks and minerals. These rocks and minerals are weathered in place or weathered and transported, and become unconsolidated material on the surface of the earth. This material is called regolith. The upper part of the regolith is soil.

    1. Weathering breaks up rock and minerals, changes their chemical composition and characteristics, and also synthesizes a soil from the upper part of the regolith.

      This unconsolidated material is acted on by the five soil forming factors and soil is formed. For this reason the upper part of the regolith is called parent material.

      There are 5 general categories of parent material:

      1. Residual Rocks and Minerals

      2. Glacial Deposits

      3. Loess Deposits

      4. Alluvial and Marine Deposits

      5. Organic Deposits

  2. Minerals

    Definition: Mineral-- a solid, homogeneous, crystalline, chemical element or compound.

    1. Two types of minerals are found in natural systems: primary and secondary.

      • Whether the mineral is primary or secondary depends on the mode of formation and not on the mineral composition.
      • minerals that crystallize from cooling magma are called primary.
      • minerals that crystallize during the weathering of primary minerals are called secondary minerals.

    2. Important Primary Minerals

      Quartz SiO2
      Orthoclase / feldspar KAlSi3O8
      Plagioclase /feldspar (Ca,Na) AlSi3O8
      Muscovite / mica KAlSi3O10(OH)2
      Biotite / mica KAl(Mg,Fe)3Si3O10(OH)2
      Hornblende / Amphibole Ca2Al2Mg2Fe3Si6O22(OH)2
      Augite / Pyroxine Ca2(Al,e)4(Mg, Fe)4Si6O24
      Olivine (Mg,Fe)2SiO4
    3. Important Secondary Minerals
      1. Clay minerals- kaolinite, montmorillonite

      2. Non-silicates

        1. Oxides

          Fe2O3 hematite
          FeO(OH) goethite
          Al(OH)3 gibbsite

        2. Carbonates

          CaCO3 calcite
          CaMg(CO3)2 dolomite

        3. Sulfates

          CaSO4 * 2H2O gypsum
  3. Rocks

    Definition: Rock -- an aggregate of one or more minerals.

    The mineral composition of rocks determine their physical and chemical properties.
    1. Igneous rocks - Formed from the solidification of molten rock material.

    2. Sedimentary rocks - Formed from sediments.

    3. Metamorphic rocks - Modified by heat, pressure and chemical process while buried below the earth's surface
  4. Igneous Rocks

    1. Properties are a result of:

      1. Minerals in original magma; amount of SiO2
      2. Cooling (crystallizing) environment

      Remember that all rocks started out as igneous rocks

      • slow cooling deep in the earth--produces large mineral crystals
      • rapid cooling at or near the surface--produces small mineral crystals

    2. Color

      Dark Contains Plant Nutrients
      Light Contains Quartz (few plant nutrients)

    3. Texture

      Coarse Weathers slowly, usually quartz (sand)
      coarse grained igneous rock
      Fine Weathers more quickly, plant nutrients present
      fine grained igneous rock

      Broad soil interpretations may be made by understanding the composition of igneous rocks and the type of soil material derived from them.

    4. Important Soil Forming Igneous Rocks

      Texture Dark Intermediate Light
      Coarse Gabbro Diorite Granite
      Intermediate Basalt Andesite Rhyolite
      Fine Obsidian


      Igneous rocks may be the most important of the three types because the other two forms are alterations or changes of igneous rocks.

  5. Sedimentary Rocks

    Formed from the deposition and lithification of weathering products

    Cemented together with pressure and/or chemicals

    sandstone sand size grains cemented together
    shale clay size grains cemented together
    limestone (CaCO3) is calcitic / (Ca, Mg) (CO3)2 is dolomitic

    75% of the rocks that cover the earth's surface are sedimentary

  6. Metamorphic Rocks

    Formed from the alteration or preexisting rocks due to heat and/or pressure
    sandstone = quartzite
    shale = slate
    limestone = marble
    granite = gneiss


    Rock Cycle


    diagram of the rock cycle


    Interesting links to rocks and minerals

    Rocks and Minerals