ES 4901 Petrology
Lab 1
Name: _______________________________
For this lab we will build on your familiarity with rock identifications, using hand
specimens and thin sections.
Part 1. On the table is a pile of rocks. Separate them into piles of Igneous Rocks, Detrital
Sedimentary, Chemical sedimentary, Foliated Metamorphic, and Unfoliated
Metamorphic.
Next, for the Igneous Rocks, separate them by color. Mafic rocks (Basalt, Gabbro,
Diabase) are dark green to black, intermediate silica rocks (Andesites, Diorites) are salt
and pepper gray, and felsic rocks (Rhyolites, Granites) are light pink and gray.
Arrange the detrital sedimentary rocks by largest grain size and give the cutoffs for sand
size.
Arrange the metamorphic rocks by foliated and non-foliated, and arrange the
metamorphosed pelitic sediments (metamorphosed mudrocks) by grade.
Part 2. For lab homework, read all three of the Jane Selverstone PowerPoints “Optical
Mineralogy in a nutshell”. They are in your lectures folder.
Using a polarizing microscope, we will examine some thin sections. Find and identify the
common rock-forming minerals (list below), and draw their appearance in quick pencil
sketches. Note their identifying characteristics. INCLUDE Plane Polarized light (PPL)
and Crossed Polars as appropriate for your identification. On the line below, write the
slide name. Draw an arrow to the mineral you identified, and give its name.
A Michel-Levy chart is provided. For slides with Quartz, give the thickness of the section
.
Discuss the characteristics of Plagioclase, Microcline, Quartz, Amphibole, and Biotite.
Plagioclase: _________________________________________________________________
Microcline, etc. ______________________________________________________________
Quartz _____________________________________________________________________
Amphiboles (e.g. Hornblende) __________________________________________________
Biotite _____________________________________________________________________
Other (Name: _____________) _________________________________________________
How do the crystals in an igneous rock differ from those in a foliated metamorphic rock?
1 micron = 1×10−6 meter. A standard thin section is 30 Microns thick.