Lab: Identification of Minerals
Introduction:
Rocks are made of minerals. There are over 2000 different minerals on
earth but there are only about 10 that are common and make up most of the
volume of just about all rocks. These common minerals are quartz, potassium and
plagioclase feldspar, muscovite and biotite mica, calcite, amphibole, pyroxene,
hematite, and gypsum.
Minerals themselves are made up of elements and compounds of elements
that get recycled from one rock to another over time as the forces of weathering
and erosion, compaction and cementation, heat and pressure, and melting and
cooling of rock and magma change one rock into another in a never ending rock
cycle.
Minerals have characteristic composition and structure of atoms and that
gives them characteristic properties such as color, streak, luster, hardness, density,
magnetism, cleavage, crystal form and acid reaction.
By making careful observations of the physical properties of minerals
they can be identified. This is helpful not only for mineral extraction for human
use (GOLD! DIAMONDS! SHINY PRECIOUS METALS) but also for
identification of rocks. With a little more knowledge conditions on earth when
they where they formed can also be determined once you know the rocks and
minerals present.
Methods:
1. Look at your mineral samples. Notice that there are two samples of mineral 1 (1
that displays its characteristic crystal shape and 1 that shows a broken piece of
the mineral without a crystal shape) and two samples of mineral 14 (1 purple and
1 green to show the two colors and also to show what the cleavage planes can
look like in this mineral)
2. Fill in the color column of data chart based on observation.
3. Fill in the streak column of the data chart using the streak plate. Note that for
minerals harder than the streak plate there will be no streak color and for light
colored minerals the streak will either be white. Mainly streak is important for
the metallic minerals.
4. Fill in the luster column of the data chart based on observation.
5. Fill in the hardness column of the data chart as “soft 1-3” if you can scratch it
with your finger nail, “hard 6.5-10” if it can scratch glass, and “medium 3-6.5” if
it is harder than your fingernail but softer than glass. Sample 6 and 7 are too thin
to test their hardness, they have a hardness of “medium.” Note, there are 2
samples of sample #4, the clear one should not be scratched for hardness.
6. Fill in the fracture vs. cleavage column by looking for very flat surfaces that are
not crystal faces. If there is no flat surfaces than the mineral has “fracture,” flat
surfaces indicate “cleavage”
7. Check the minerals for special properties like magnetism, reaction to HCL (only 1
drop per sample…wash your hands immediately if you get the HCL on them),
smell, double refraction etc. and note any special properties you found in the
column marked “special properties.” Note, there are 2 samples of sample #4, the
clear one should not be scratched or had acid dripped on it!
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8. Use the mineral ID chart to fill in the column for mineral name and chemical
formula.
9. Answer the analysis and conclusion questions.
Analysis & Conclusion Questions
1. Look at your mineral samples. Mineral 1 and mineral 15 are the same mineral.
Mineral 14 has two different samples that are the same mineral. Minerals 2 and 3
are the same mineral. What characteristic is NOT helpful in identifying these
minerals?
2. There are 5 minerals in a row that all have “metallic” luster. What #s are they?
3. There are 2 minerals that have perfect single direction cleavage planes which
make them peel in sheets. Which mineral numbers are they?
4. There are 4 other samples with visible cleavage planes. What numbers are they?
5. Which minerals show crystal form?
6. Which minerals were the easiest to identify/know for sure you identified them
correctly? Why?
7. Which minerals were the hardest to identify/know if you got correct? Why?
8. Which two minerals might you easily mix up? Why? What characteristic will
help you make sure to identify them properly in the future on a quiz?
9. Silicates are minerals that contain SiO2 …Which samples of yours are silicates?
10. Why are so many minerals silicates?
11. Minerals that contain metal are valuable to people. Which of your minerals are
metal bearing minerals?
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