Influenced largely by chemical composition and
atomic structure of the mineral

I. Color and Some Related Properties of Minerals
Minerals are colored because certain wavelengths of light are absorbed, and the mineral color
         then results from the combination of those wavelength which reach the eye--if light is not
         absorbed, the mineral is colorless in reflected or refracted light and is black if all wave-
         of light are absorbed--pleochroism may be present in certain minerals if light travels
         along crystallographic axes--a mineral may display more than one color when rotated or viewed
         at different angles--cordierite specimens often display a clear-white and violet color when
         rotated indicating a dichroism quality.

Idiochromatic color-mineral color caused by the presence of element(s) in the chemical composition of the mineral
   -Cu in azurite (blue); Cu in malachite (green); Mn in rhodonite and rhodochrosite (pink)-

Chromaphore color-caused by the presence of a small concentration of element(s) (Fe, Mn, Cu, Cr, Co, Ni, V) or which do not comprise the chemical composition of the mineral--these elements
 are called chromophores
   --Cr and V in beryl--deep green of emerald; Fe in quartz--purple of amethyst; V in zoisite--rich sapphire blue--

   A.  Electron and Molecular Transitions---idiochromatic and chromaphore elements can 
                                                                        cause color by the following mechanisms:
       1. Crystal Field Transitions
            wavelength of light quanta are absorbed by "d" electrons in transition elements result-
            ing in transmissions of wavelengths of light giving the mineral it's color
                 Transition Element                Mineral      Resulting Color of  Mineral
                         Cr+3 beryl-Be3Al2Si6O18--emerald                 green
                         Cr+3 corundum-Al2O3--ruby                  red
                         Mn+2 beryl-Be3Al2Si6O18-morganite                  pink
                         Fe+2 olivine-(Mg,Fe)2SiO4-peridot                  yellow-green
         2.   Molecular Orbital Transitions 
                    metal ions undergo charge transitions or electron 'hopping'

                    Transition                            Mineral                              Resulting Color of Mineral 
                    Fe+2 > Fe+3             beryl-Be3Al2Si6O18-aquamarine              blue to yellow    
                    Fe+2 > Ti+4              corundum-Al2O3-sapphire                       blue
    B.  Inclusions of Other Minerals
green quartz caused by chlorite dispersions--
black calcite caused by MnO2 dispersions--
red color in many minerals caused by hematite dispersions--

    C.  Special Mineral Properties Related to Light, Heat, and Electricity
1. Play of Colors (Iridescence)
                  -results from diffracted and reflected light from closely spaced fractures, cleavage
                    planes, exsolution, or minute inclusions in parallel orientation-- 
                        in opal--reflected light from submicroscopic layers of spherical SiO2 particles
                        in labradorite--reflected light from exsolution laminae

          2. Chatoyancy
                 -silky or wavy appearance in minerals caused by closely packed parallel fibers
                         in satin spar--gypsum
                         in cat's eye--chrysoberyl 
                         in tiger's eye--quartz

          3.  Asterism
               -a star like figure appearing on the surface of a mineral caused by reflection or scattering of 
                light off needle inclusions of minerals which parallel crystallographic axes
                          rubies and sapphires--corundum

          4.  Luminescence
               -a special glowing of the mineral caused by the presence of impurities (activators) in a mineral

               a.   Fluorescence
                   -emission of light wavelength caused by electron excitation in transition metals
                      during bombardment of a mineral with ultraviolet or x-rays-- examples are:
                            some specimens of fluorite, scheelite, calcite

               b.   Phosphorescence
                   -continuous emission of light wavelength after the excitation source is removed-
                             similar mineral specimens as given in fluorescence above

          5.  Thermoluminescence
                -emissions of light wavelengths when mineral is subjected to heat below the "red hot"
                  temperature--examples are:
                               some specimens of calcite and apatite

          6.  Piezoelectricity
                -a flow of electrons in mineral crystals by simply exerting a compressive pressure at both
                  ends of the "c" axis of crystals which have no center of symmetry-- examples are:
                               quartz and tourmaline

          7.  Pyroelectricity
                -same as piezoelectricity except stimulated by heat

II.  Hardness 
     A. Moh's Hardness Scale
a listing of minerals with increasing relative hardness 1-10-
             1. talc                 6. feldspar
             2. gypsum           7. quartz
             3. calcite             8. topaz
             4. fluorite            9. corundum
             5. apatite         10.diamond
the following can be assigned a hardness in this scale-
              glass = 5.5;   knife = 5.5 steel file = 6-7 fingernail = 2.5;  penny = 3
          -the hardness of a mineral can differ slightly in the direction of scratching--kyanite between
           a hardness of 5 to 7, and calcite between 2 and 3

III. Tenacity
the cohesiveness of a mineral, or the resistance a mineral offers to breaking, crushing,
         bending or tearing--
       1. brittle--if a mineral powders easily
       2. malleable--if a mineral can be hammered into sheets
       3. sectile--if a mineral can be cut into thin shavings with a knife
       4. ductile--if a mineral can be drawn into wire
       5. flexible--if a mineral is bent but does not resume the original shape
       6. elastic--if a mineral bends and resumes the original shape

IV.  Streak
is the color of the powder from the mineral on a porcelain plate (streak plate)--
        --since most minerals are softer than porcelain (8 hardness on Moh's Scale), their powder 
           will remain after scratching it on the streak plate

V.  Luster
--is the general appearance of the surface of a mineral in reflected light--minerals can have
           a metallic luster if they are opaque to light, give a prominent dark or black streak, and are
           usually dense like galena, pyrite, and bornite or can have a non metallic luster if they are 
           translucent or transparent to light and have a colorless or white streak
        --on occasion it is difficult to determine if a mineral is one or the other and may have a
           sub metallic luster
        --some specific types of non metallic lusters are:
              1. Vitreous-resembles glass--quartz crystals
              2. Resinous-resembles a resin--sulfur and sphalerite
              3. Pearly-pearl-like and present on mineral surfaces paralleling cleavage planes--talc
              4. Greasy-appears to be covered by oil or grease--massive quartz
              5. Silky-silk or satin-like--satin spar gypsum
              6. Adamantine-brilliant looking minerals which have a high index of refraction--diamond

VI. Cleavage, Parting, Fracture, Specific Gravity and Crystal Habit
       A.  Cleavage
             -the ability of a mineral to break or come apart in a consistent way--breakage is along
              atomic planes-cleavage is consistent with crystal symmetry and may be one to multi-
              directional from one mineral to another-
                     --micas = one direction of cleavage
                     --feldspars, pyroxenes and amphiboles = two directions of cleavage
                     --calcite and dolomite = three directions of cleavage (rhombohedral)

              -cleavage may be of various qualities as perfect, good, fair or poor but the same
                cleavage quality and quantity will be present in all specimens of the same mineral
              -the presence of cleavage in a mineral is often observed by reflecting light off a fresh
               surface and observing a stair like arrangement of thin parallel layers

      B.  Parting
            -breakage of minerals along planes of structural weakness such as twinning planes
            -unlike cleavage, parting is not shown by all specimens of the same mineral but
              only those which are twinned or formed under special pressure conditions

      C.  Fracture
            -the inability of a mineral to break in a consistent way and therefore not along cleavage
            -a few specific types of fracture are:
                   1.   Concoidal- a smooth, curved breakage--quartz
                   2.   Fibrous or Splintery
                   3.   Hackly-jagged with sharp edges
                   4.   Irregular-rough surfaces

       D. Specific Gravity
             -a number that expresses a ratio between a substance and the weight of an equal volume
              of water at 4 degrees C--the number is the same for that of the density without units
             -specific gravity (S.G.) depends on (1) the kind of atoms comprising a mineral (atomic
              weight) and (2) the packing of the atoms (close packing or loosely packed)
             -S.G. can be measured with a Jolly Balance which determines the weight of a mineral in
              air and the loss of weight in water--the S.G. number is then obtained by dividing the
              weight in air by the loss of weight in water
             -S.G. can also be calculated--

      E. Crystal Habits and Aggregates
the appearance of a single crystal or an aggregate of crystals of a mineral can aid in the
            identification of the mineral
             1.  isolated individual mineral crystals
                  a. bladed-elongated flattened crystals looking like a knife blade
                  b. acicular-thin needlelike crystals
                  c. capillary-hair like or thinner

              2. groups of distinct crystals
                  a. dendritic-resembling small veins on a tree leaf
                  b. radiated-crystals appearing in a radial pattern
                  c. drusy-a surface containing very small crystals

               3. groups of distinct crystals occurring in parallel or spherical form
                   a. columnar-column like crystals
                   b. bladed-many flat bladed crystals
                   c. fibrous-parallel fibers
                   d. colloform-includes botryoidal ( resembling a bunch of grapes), reniform (kidney-
                        shaped masses, and mammillary (mammae masses)

               4. aggregate of scales or lamellae
                   a. foliated (micaceous)-easily splits into thin leaves or sheets
                   b. plumose-scaley-featherlike structure

               5. granular aggregate
                    comprised of an aggregate of equant grains

               6. other types
                   a. pisolitic and oolitic-rounded masses of pea size grains (pisolitic) or very small
                       grains (oolitic)
                   b. stalactitic-resembling stalactites
                   c. massive-massive with no form or distinguishing features
                   d. geode-rock cavity filling with mineral crystal
                   e. banded-a mineral showing narrow bands of different colors or textures

           use the physical properties discussed above and Determinative Tables (page 584) and/or
           computer program supplied in lab to determine the name of a series of unknown minerals
           given to you during the semester----the Mineral Index (page 619) will also be important to you


bladed (selenite gypsum)
bladed(gypsum).jpg (27506 bytes)

acicular (stibnite)
acicular(stibnite)1.jpg (8060 bytes)

  radiated (wavelite)
radiated(wavelite).jpg (24094 bytes)

  drusy ( tiny quartz crystals)
drusy(quartz).jpg (18509 bytes)

  fibrous (crysotile-serpentine)
fibrous(crysotile).jpg (34580 bytes)

  colloform (botryoidal hematite)
colloform(hematite).jpg (22017 bytes)

  foliated (micaceous)
micaceous(muscovite).jpg (17436 bytes)

  granular (chromite)
granular(chromite)(.jpg (11978 bytes)

  pisolitic (bauxite)
pisolitic-oolitic(bauxite).jpg (18964 bytes)

  stalactitic (goethite-limonite)
stalactitic(goethite-limonite).jpg (22835 bytes)

  massive (magnetite)
massive(magnetite).jpg (21486 bytes)

   geode (quartz crystals)
geode.jpg (24718 bytes)

  banded (hematite)
banded(hematite).jpg (23061 bytes)

   tigers eye
tigers eye.jpg (8955 bytes)

   bladed group (barite)
grpblades(barite).jpg (25456 bytes)