EARTH SCIENCE LAB
Mineral Physical Properties and Identification
Link:
http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/minerals/
Minerals
Minerals are defined as naturally occurring, inorganic, solids with a definite chemical
composition and a regular, internal crystalline structure. The keys to this definition are the
chemical composition and the crystalline structure. Different chemical compositions result in
different minerals. A good example is the mineral plagioclase. Plagioclase is a member of the
feldspar group, but there is more than one type of plagioclase. Albite and anorthite are two
examples. Albite has a chemical composition of NaAlSi3O8, while anorthite's chemical
composition is CaAl2Si2O8. Very similar, but different - therefore two different minerals.
Different crystalline structures, or how the atoms and molecules are arranged, result in different
minerals. A good example is diamond and graphite. Both minerals are composed of carbon (C).
The same chemical composition, but two different crystalline structures - therefore, two different
minerals.
Physical Properties
Determination of the actual chemical composition and crystalline structure of a mineral is
difficult without the proper equipment. In an introductory level lab it is impossible for us to
determine these two aspects of a mineral. Fortunately, these two aspects determine a mineral's
physical properties. How the atoms and molecules are arranged and the strength of the bonding
between the atoms result in different physical properties for different minerals. While many
minerals share common physical properties, when all of a mineral's physical properties are
examined, it often results in a unique set of physical properties which can be used to identify the
mineral.
Below you will find a chart which defines the physical properties and provides the means for
determining the physical property of a mineral sample. These definitions and methods are
simplified. Consult your lab manual for detailed discussion.
Mineral Physical Properties Chart
PHYSICAL
PROPERTY
Cleavage
Definition*
Testing Method
Examine the mineral for areas where the mineral is
broken. Look for areas where the light reflects from
Breakage of a mineral
planar surfaces. This can be easily confused with a
along planes of weakness
crystal face and is the most difficult properties for
in the crystal structure.
students to master
Visible light spectrum
Look at the sample and determine its color - white,
radiation reflected from a black, green, clear, etc.
mineral.
Examine and describe the geometric shape of the
Geometric shape of a
Crystal Form
mineral - cubic, hexagonal, etc. Not commonly seen in
crystal or mineral.
most introductory lab samples.
Breakage of a mineral, not Examine the mineral for areas where the mineral is
Fracture
along planes of weakness broken. Describe the breakage as either irregular or
in the crystral structure.
conchoidal (has the appearance of broken glass)
Use minerals of known hardness from the Mohs
Hardness Kits. Scratch the unknown mineral with a
Resistance to scratching or
Hardness
known hardness to determine which mineral is harder.
abrasion.
Continue doing this with harder or softer minerals from
the kit until the hardness is determined.
Look at the sample to determine if the mineral is
Character of the light
Luster
metallic in appearance (looks like a chunk of metal) or
reflected by a mineral.
non-metallic (doesn't look like a chunk of metal).
Electromagnetic force
Use a magnet to determine if the magnet is attracted to
Magnetism generated by an object or
the sample.
electrical field.
Chemical interaction of
Place one small drop of HCl on a sample a watch for a
Reaction to hydrochloric acid and
reaction - effervesces (bubbles).
HCl
calcium carbonate
(CaCO3).
Ratio of the mass of a
Generally not determined in an introductory lab. Look
Specific
mineral to the mass of an this information up in your lab manual once the mineral
Gravity
equal volume of water.
has been identified.
Grind a small amount of a mineral into a powder on a
Color of the mineral when
Streak
porcelain streak plate and determine the color of the
it is powdered.
powder.
Nerve ending reaction in Lick the mineral. (not recommended in an introductory
Taste
the tongue to different
lab - you don't know who has handled or licked the
chemicals.
sample before you).
Requires special equipment such as a UV lamp and
Other
Fluorescence,
geiger counter. These are not commonly tested for in an
Properties
Radioactivity
introductory lab.
* Definitions simplified or modified from Bates, R.L. and J.A. Jackson (eds.), 1987, Glossary of
Geology. American Geological Institute, Alexandria, VA, 788 p.
Color
Below is a table listing some of the aspects of the common lab minerals. This table is not a
complete listing of all of the physical properties for each mineral. It is designed to highlight
those physical properties that are unique to that mineral or assist in identification of that mineral.
Be aware that not all mineral samples will necessarily show these physical properties. For
example, all plagioclase has cleavage. The sample you examine may or may not show that
cleavage. All minerals have a crystal form. However, rarely do introductory mineral samples
show a good crystal form. Some types of minerals rarely show a crystal form and even museum
collections may not contain good examples of a mineral's crystal form.
Mineral Identification - Diagnostic Physical Properties
Apatite
Green color, H=5, may show hexagonal crystal form
Dark or dull green color, 2 cleavages at ~90 degrees, similar properties to
Augite
Hornblende
Black color, one perfect direction of cleavage resulting in the mineral pealing into
Biotite
thin, flexible sheets, similar properties to Muscovite
Calcite
H=3, reacts with HCl, 3 directions of cleavage (rhombic cleavage)
Corundum H=9, often shows hexagonal crystal form
Dolomite Reacts to HCL in its powdered form, similar properties to calcite
H=4, 4 directions of cleavage, often purple in color (can be white, clear, yellow,
Fluorite
green)
Galena
Gray, metallic mineral, 3 directions of cleavage (cubic)
Typically reddish brown color, no cleavage, commonly found in twelve-sided
Garnet
crystals (dodecahedrons)
Graphite "Pencil lead", soft metallic mineral, gray streak
Gypsum
H=2, can be scratched with a fingernail
"Salt", H=2.5, cannot be scratched with a fingernail, 3 directions of cleavage (cubic),
Halite
salty taste
Hematite Reddish brown streak, "rust"
Black to dk. green color, 2 directions of cleavage at 120 or 60 degrees, similar
Hornblende
properties to Augite
Magnetite Magnetic, metallic mineral
Clear or translucent color, one perfect direction of cleavage resulting in the mineral
Muscovite
pealing into thin, flexible sheets, similar properties to Biotite
Apple green or yellowish green color, H=7 (often difficult to determine), conchoidal
Olivine
fracture, no cleavage
H=6, salmon pink color is typical, perthitic intergrowths are common, 2 directions of
Orthoclase
cleavage at 90 degrees, similar properties to plagioclase
H=6, white or gray color, striations may be seen on cleavage surface, 2 directions of
Plagioclase
cleavage at 90 degrees, similar properties to orthoclase
Pyrite
"Fool's Gold", gold metallic color
H=7, conchoidal fracture, no cleavage, color is typically white or clear but can be
Quartz
pink, red, purple, black
Sulfur
Yellow color, "rotten egg" smell if burned
Talc
H=1, very soft, easily scratched by fingernail
On each of the following pages you will find an image of a mineral and a series of physical
properties tests. Identify the physical properties that are present. Once this is done, identify the
mineral. It is recommended that you use your lab manual during these exercises as detailed
identification information is not given in these web pages. Click each answer, then check to see
if you have correctly identified the mineral sample.
Use Data Table to record the data you collect as you work through identifying your samples
Mineral Names
Apatite
Corundum
Garnet
Hematite
Olivine
Quartz
Augite
Dolomite
Graphite
Hornblende
Orthoclase
Sulfur
Biotite
Fluorite
Gypsum
Magnetite
Plagioclase
Talc
Calcite
Galena
Halite
Muscovite
Pyrite