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Unit Two - Geochemical Methods
3. Geochemical Testing
Lab Activity
Objectives:
Part 1: Use the flame color test to distiinguish between
the minerals galena and stibnite.
Part
2: Use the following flame tests to confirm the presence of
the elements in the minerals listed:
|
Flame Test
|
Element
|
Mineral
|
|
Odor
|
Arsenic
|
Arsenopyrite
|
|
Bead
|
Copper
|
Chalcopyrite
|
|
Thermoluminescence
|
-
|
Fluorite
|
|
Charcoal
|
Molybdenum
|
Molybdenite
|
|
Magnetism on Heating
|
Iron
|
Hematite
|
Table
T5:
Flame test techniques, elements, and mineral samples.
- Minerals:
- Galena, stibnite, arsenopyrite, chalcopyrite, fluorite, molybdenite,
hematite.
- Propane
torch
-
Charcoal block
-
Hydrochloric acid
-
Platinum wire loop and holder
-
Sodium carbonate
-
Pencil magnet
-
Ultraviolet light
-
Borax
Procedure:
Part
1: In advance the teacher needs to take a small amount of stibnite
and a small amount of galena and crush the minerals. Notice how
difficult it is too tell these minerals apart if the cleavage is
not obvious.
1.
Grind the two minerals into separate powders.
2.
Use the flame color test directions.
Stibnite contains antimony. Antimony yields a pale green flame
color.
Galena contains lead. Lead yields a light blue flame color.
Part
2: Follow the directions for each of the different types of
flame techniques listed in Table T5. Confirm
the presence of each element (or mineral) listed by documenting the
results:
Arsenic:
Garlic odor.
Copper:
| |
Color
from Oxidizing Flame
|
Color
from Reducing Flame
|
|
Hot
Bead
|
Green
|
Opaque
to dk brown
|
|
Cold
Bead
|
Blue
|
Colorless
to green
|
Fluorite: Luminesces upon mild heating. Do the test
in a dark room.
Molybdenum:
Test a small grain on the charcoal. Heat with oxidizing
flame and observe these results:
- Sublimate
forms which is yellow near grain and blue further away.
- Upon
cooling the blue sublimate turns white.
- Upon heating briefly
with reducing flame, the white sublimate turns blue.
Iron:
Hematite becomes magnetic.
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