Lab 3: Introduction to the Optical Mineralogy
Name _______________________
1. Your instructor will pass around a cleavage rhomb of transparent
Calcite. Please be very careful not to drop this specimen. Place the
Calcite over printed text, then rotate the Calcite. Pass the Calcite to
the next student, then describe what you saw:
2. Your instructor will place an Olivine Porphyry thin section on the
Leitz Microscope.
a. Explain how to distinguish Olivine from Plagioclase.
b. Look at the slide in plane polarized light with Olivine and
Plagioclase in the same field. Compare the relief.
c. Explain the difference in relief .
d. Why are the Olivine xenocrysts larger than most of the
Plagioclase crystals?
3. Your instructor will place a Muscovite-Biotite Granite thin section on
the Leitz Microscope. It contains Quartz, Microcline (similar to
Orthoclase ), and a high-sodium Plagioclase. Write down the
recognition features for each here:
4. Your instructor will place a Sillimanite-Garnet Gneiss thin section on
the Leitz Microscope.
a. The Garnets are Isometric, and are therefore Isotropic. Explain
how to find an Isotropic mineral under crossed Polarizers.
b. Can you find any other minerals you recognize?
In your locker is your microscope. Inventory the parts, get a light if needed.
5. Igneous and Metamorphic rock thin sections are in the front of the
room. Read the description, then examine them with plane polarized
and cross polarized light. With your microscope, look for minerals
you have seen today, and sketch the view here.
Provide labels for identified minerals outside the circles, and point to them
with arrows.
Turn this in next class.