Objective: To be able to identify minerals by collecting physical and chemical properties.
Questions:
1. Why is the color of a mineral not a reliable method of identification?
Color can be variable and inconsistent, i.e.
fluorite (#25) may be purple, yellow, white, clear, brown, blue, or green.
2. Why is the streak more reliable for mineral identification?
Streak is more reliable and consistent than
color (the streak for all colors or fluorite is white). However, only minerals
softer than the streak plate will leave a streak.
3. What is a diagnostic property and why is it useful for mineral
identification?
Diagnostic means a particularly useful property
specific for identifying a particular mineral. Most minerals have
at least 2 or 3 diagnostic properties. It takes experience to know
which physical properties are diagnostic and which are not. That's
why you systematically collected data in the lab.
4. Can most minerals be identified by just a single physical property?
No. In most cases, it takes 2 or 3 diagnostic
physical properties to distinguish one mineral from another.
5. Why should the hardness test always be performed beginning from the
"soft" end?
Starting with the steel file (H=6.5) means
that a scratched mineral can be of hardness 6, 5, 4, 3, 2, or 1; which
does not give you precise information. Starting from the softer end
of the scale (fingernail H=2.5) works much better.
6. What happens when two substances of similar hardness are ground together?
Minerals of similar hardness will barely be
able to scratch another of equal hardness.
7. Why is the acid reaction test of limited value?
The acid test only works for certain carbonates
(produces carbon dioxide "fizzing") and certain sulfides (produces hydrogen
sulfide "rotten egg" gas).
Introduction to Mineral Identification
You will be introduced to the definitions and descriptions of various
physical properties measured in minerals, including: hardness, color, streak,
luster, cleavage, acid reaction, specific gravity, etc., and you will see
a demonstration on how to use simple laboratory equipment to perform these
tests. You will be assigned a set of 5 different mineral specimens. Using
the test equipment and the correct technique, test for each of the physical
characteristics in all 5 specimens, and fill in each data column in the
table below. (Tip: Fill out the table vertically in columns,
not across in rows - this way, you will practice your laboratory technique
for each type of test.) After you have listed the properties, consult
the mineral identification tables booklet and identify each mineral. Check
with your instructor when you have finished.
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(rotten egg smell) |
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"fizzing" |
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