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Earth Science Laboratory
EAS 100-51 : Lab 1
TESTING PHYSICAL PROPERTIES FOR MINERAL IDENTIFICATION

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.
No.
Color
Streak
Luster
Hardness
Cleavage
(if present)
Acid Rx
Other Properties
Mineral Name
"A"
#20
silver gray 
black  
metallic 
2.5 
3-directions, at 90 degrees 
hydrogen sulfide
(rotten egg smell)
high specific gravity 
galena 
"B"
#8
brassy yellow 
brownish-black
metallic 
6 - 6.5 
NONE 
NONE 
high specific gravity 
pyrite 
"C"
#25
 variable
white
vitreous
 4
4 directions 
NONE 
 
fluorite 
"D"
#3
 white/colorless
white 
vitreous 
3 directions, NOT at 90 degrees (rhombic) 
carbon dioxide
"fizzing" 
 
calcite 
"E"
#4
 colorless
white 
vitreous 
2.5 
3 directions, at 90 degrees 
NONE 
tastes salty 
halite