Common Rock-Forming Minerals:
Identification
Minerals are the building blocks of rocks.  They are the natural expression of the chemical composition of rocks, hence the natural expression of the chemical composition of the crust of the Earth and most of the mantle.  By definition, a mineral has the following attributes:
  1. NATURALLY OCCURRING
  2. INORGANIC
  3. CRYSTALLINE
With regard to the last attribute, it necessarily follows that a mineral has a specific chemical composition or a restricted range of chemical composition.  The composition of a mineral can be expressed as a CHEMICAL FORMULA, which simply gives the proportions of the different elements and groups of elements in the mineral.  The latter notion (groups of elements) comes into play for those minerals which have a restricted range of composition.  QUARTZ is a good example of a mineral with a specific chemical composition, SiO2.  The chemical formula means that in quartz, the ratio O:Si is always 2:1. OLIVINE, on the other hand, is a good example of a mineral with a restricted range of composition.  It's chemical formula can be written (Mg,Fe)2SiO4.  The chemical formula means that the ratio O:Si:(Mg+Fe) is always 4:1:2.  The composition can very over a specific range from Mg2SiO4 to Fe2SiO4.  The composition of a particular olivine will depend on the chemical environment in which it formed.  If the environment, say a magma, has a high Mg:Fe ratio, the resulting olivine will have a high Mg:Fe ratio.  Conversely, the composition of a mineral (e.g., Mg:Fe in olivine) tells us something about the chemistry of the environment (e.g., Mg:Fe in a magma).  Details such as this, pertaining to minerals with restricted ranges of compositions, can also provide information about the pressure and temperature of the environment in which a mineral formed.  Whenever two or more elements are enclosed in parentheses in a mineral formula, the composition of the mineral is variable over a restricted range expressed by the individual elements in parentheses.

In this exercise you will learn to identify common rock-forming minerals.
 

Mineral Classification
Classification schemes for minerals are based on two main criteria, CHEMICAL COMPOSITION and CRYSTALLINE STRUCTURE.  In this lab exercise you will be examining minerals from the following chemical groups, and structural subgroups:
 
CHEMICAL GROUP ANIONIC SPECIES EXAMPLES
OXIDES minerals Oxygen, O-2 Hematite, Fe2O3; Magnetite; Fe3O4
SULFIDE minerals Sulfur, S-2 Pyrite, FeS2
CARBONATE minerals Carbonate, CO3-2 Calcite, CaCO3; Dolomite, CaMg(CO3)2
SILICATE minerals Silicate, SiO4-4 , "Tetrahedron"  
 
STRUCTURAL
SUBGROUPS
OF THE 
SILICATES
 Isolated SiO4-4 Tetrahedra Olivine, (Mg,Fe)2SiO4;
Garnet, (Fe,Mg,Ca)3Al2Si3O12
Single Chains of Tetrahedra, Si2O6-4 Pyroxene, e.g., Augite, Ca(Mg,Fe)Si2O6
Double Chains of Tetrahedra,
   (Si,Al)8O22-12 to -14		 Amphibole, e.g.,  Hornblende,
    NaCa2(Mg,Fe,Al)5(Si,Al)8O22(OH)2
Sheets, (Si,Al)4O10-4 to -6 Micas (phyllosilicates), e.g., 
    Muscovite, KAl2(AlSi3)O10(OH)2,
    Biotite, K(Mg,Fe)3(AlSi3)O10(OH)2,
    Chlorite, (Mg,Fe)6Si4O10(OH)8
Framework, 
    SiO2 or (Al,Si)O2-.25 to -0.5		 Quartz, SiO2
Feldspars
    K-Feldspar, K(AlSi3)O8
    Plagioclase, (Na,Ca)(Al,Si)4O8

 
 
PROPORTIONS of MINERALS in CONTINENTAL CRUST

Physical Properties
The PHYSICAL PROPERTIES of a minerals are determined by (1) Crystalline State, (2) Composition, and (3) Grain size and shape.  Thus physical properties can be used to identify or classify minerals.  For routine mineral identification the important physical properties are as follows:
 
LUSTER Appearance in reflected light.  For the purposes of this exercise, there are three main lusters:
  METALLIC,  appearance of shiny, polished metal.
  SUBMETALLIC, appearance between glass and metal or dull metal. 
  NON-METALLIC, many descriptive terms, but most common are:
    VITREOUS (glassy), like glass; and 
    EARTHY (like dirt, or other powdery materials).
COLOR and SHADE COLOR refers to the hue (red, orange, yellow, green, blue, etc.).
SHADE refers to the relative darkness of the color (dark colored, light colored).
HARDNESS Resistance of the mineral to scratching is measured using the MOHS hardness scale.  In this scale, 
  your FINGERNAIL has a hardness of 2.5 (H=2.5), 
  a COPPER PENNY has a hardness of 3 (H=3), and 
  ordinary window GLASS has a hardness of 5.5 (H=5.5).
CLEAVAGE Where a mineral breaks along smooth, flat surfaces.  Some minerals such as quartz show NO CLEAVAGE.  Other minerals show 1-WAY CLEAVAGE (micas, breaks into thin sheets or flakes), 2-WAY CLEAVAGE (feldspars, pyroxenes, amphiboles), or even 3-WAY CLEAVAGE (calcite, dolomite).
STREAK Color of the mineral when it is powdered.  The test is done by rubbing the mineral on a streak plate (Hardness = 6.5).  Minerals softer than 6.5 leave a mark on the plate.  The STREAK is described by hue and shade.
 
SPECIAL PROPERTIES
  Specific Gravity, s.g. Technically, s.g. is the ratio of the weight of the mineral to the weight of an equal volume of water.  The average s.g. for minerals is about 2.7, or 2.7 time heavier than an equal volume of water.  For routine mineral identification, you need only to have a sense of whether the mineral is LIGHT, AVERAGE, or HEAVY.
Dilute HCl acid This test is for the carbonate minerals, calcite and dolomite.  These minerals react with dilute HCl. A drop of dilute HCl on calcite EFFERVESCES (fizzes) vigorously.  Dolomite reacts less vigorously.  Normally dolomite fizzes only weakly even when the mineral is powders.  Other minerals in this exercise do not react with HCl.
Magnetism Some minerals, such as MAGNETITE, containing Fe and depending on the form the Fe, are attracted strongly to a magnet.
Odor When rubbed on a streak plate, most SULFIDE minerals give off a rotten-egg odor.  When breathed on gently, CLAY minerals give off an earthy, musty odor.
****MINERAL STRUCTURES****
 On line Resource, University of Wisconsin, Madison, Materials Research Science and Engineering
IDENTIFY MINERALS
Mineral specimens are provided for examination and identification.  For each mineral, give the name and chemical formula, using the identification chart provided in this  exercise.  Using the chart is self-explanatory.  The order of observations is LUSTER, SHADE of color, HARDNESS relative to glass (H=5.5), CLEAVAGE.  At this stage the choices should be narrowed down to as few as two possibilities, or as many as five possibilities.  Examine the specific mineral properties of each of the candidate minerals to make your final identification.  The chart is set up for you to use in either of two ways:  (1) You may work through the classification process directly on the initial page, or (2) if you prefer, you may work through the classification process by responding to the questions at the bottom of each page.

[CLASSIFICATION CHART]

Designed by R.N. Abbott, Jr., Department of Geology, Appalachian State University, Boone, NC 28608, as modified from Abbott, R.N., Jr., Callahan, J.E., Cowan, E.A., McKinney, F.K., McKinney, M., Raymond, L.A., and Webb, F, 2000, Laboratory Problems in Physical Geology, 11th edition, Department of Geology, Appalachian State University, Boone, NC.