GEOLOGY 250 MINERALOGY
LABORATORY # 8
BIAXIAL MINERAL OPTICS
Minerals that belong to the orthorhombic, monoclinic, and triclinic systems have two optic axes. The biaxial indicatrix is a triaxial ellipsoid. The indices are designated ·n alpha, n beta, and n gamma; where: n alpha < n beta < n gamma
This lab includes:
A.
Birefringence
B. Biaxial Interference
Figures **i.
Acute Bisectrix Figures **ii. Obtuse Bisectrix figures
C. Determination of
2V
D. Centered Optic
axis Figures
E. Determination of
Optic sign in Biaxial Minerals
F. Dispersion
G. Sign of elongation
H. Plechroism
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