Igneous Petrology (EPSC-423A): Lab 1: Minerals in Thin Section – Francis, 2013
IGNEOUS PETROLOGY – EPSC 423
LAB #1 Igneous Rock-Forming Minerals in Thin Section
(report due by 12:30 pm Sept. 12)
The object of this laboratory is to reactivate your skills with a petrographic microscope
and have you review the optical properties of the common rock-forming minerals in
igneous rocks. To this end, identify the indicated minerals in the following slides from
the list:
Mafic
Felsic
Other
olivine
clinopyroxene
orthopyroxene
amphibole
biotite
quartz
nepheline
K-feldspar
plagioclase
volcanic glass
apatite
For each indicated unknown mineral, determine its:



optic character (isotropic, uniaxial, or biaxial),
birefringence, optic sign, and 2V (if biaxial)
any other optic features of note, such as extinction angle, pleochroism, etc.
Finish by naming the mineral. In the case of plagioclase, determine as accurately as
possible its An content using one or more of the extinction angle methods from
Spectroscopy of Minerals.
Note: A number of minerals appear more than once.
A) Sections EX 10.n
1. The flesh coloured, weakly pleochroic phenocrysts.
2. The red brown, strongly pleochroic phenocrysts and mantles on #1.
3. The low birefringence, twinned laths.
B) Sections EX-12.n
4. The large colourless euhedral phenocrysts.
5. The large light grey euhedral phenocrysts.
Igneous Petrology (EPSC-423A): Lab 1: Minerals in Thin Section – Francis, 2013
C) Sections EX- 2 to 8
6.
The abundant colourless, low birefringence (1st order colours) mineral.
7. The zoned purplish-green-grey mineral.
8. The low birefringence (1st order colours) mineral occurring as small inclusions
in #6.
D) Sections XE-n
9. The turbid brownish crystals.
10. The high birefringence clear crystals.
E) Sections M-10, M-13
11. Low birefringence (1st order colours) turbid mineral.
12. Higher birefringence (2nd order colours) turbid mineral.
F) SF 44, SF 49, SG-20, SG-35
13. The strongly pleochroic mineral.
14. The low-birefringence (1st order colours) mineral with fine exsolution
lamellae.
G) PY-n, GR-4
15. The pale brown phase at one end of the slide.
16. The low birefringence (1st order colours) needles.