BAB VII PENGAMATAN MIKROSKOP
DENGAN SISTEM KONOSKOPIK
BIAXIAL
Birefringence (), Retardation(), and Interference Colors
Uniaxial Biaxial
or
(+) OA Figure with plate
Yellow in NW is (+)
(+) OA Figure without plate
(-) OA Figure with plate
Blue in NW is (-)
(-) OA Figure without plate
(same as (+) figure)
Optical Properties of Biaxial Minerals
Sections of Uniaxial Indicatrices
= - = 0 (circular section)
= - (random section)
= - (principal section) maximum birefringence
Total
extinction in
x-polar light
Biaxial Crystals
B(+) defined as Z (g) = Bxa
B(-) defined as X (a) = BxO
g
a
OA OA
Biaxial Crystals
Acute angle between OA's = 2V
The axis that bisects acute angle = acute bisectrix = Bxa
The axis that bisects obtuse angle = obtuse bisectrix = Bxo
Optical Indicatrices A 3-d map of the indices of refraction for various vibration directions of light rays
Orientation of the indicatrix within a mineral is symmetrical with the crystallographic
axis
Isotropic
Isometric
Anisotropic Uniaxial
Tetragonal
Hexagonal
Anisotropic-
Biaxial Orthorhombic
Monoclinic
Triclinic
Circular Sections and Optic Axes
Circular Section
Circular Section
Optic Axes
Optic Plane
Biaxial Indicatrix
Principal
vibration
axes
greatest n
lowest n
intermediate n
a
Biaxial(+) Interference Figure
Biaxial Optic Axis Figures
Biaxial (+)
Acute Bisectrix Figures (Bxa)
Melatope (emergence of optic axes)
Determining the Optic Sign of Biaxial Minerals
D
+
D
- U
U
D
D
D
D
a is fast ray
is intermediate
g is slow ray
-
+ U
U
U
U
Estimating 2V by Curvature of Isogyre
Estimating 2V by Separation of Isogyres
Biaxial Optic Sign
Centered Bxa 2V = 35o
Centered Bxa 2V = 35o
With accessory plate
Biaxial Interference Figures
Same figure rotated 45o
Optic axes are now E-W
Clearly isogyres must swing
Biaxial Interference Figures
Sign of Elongation
g
Slow ray Fast ray
a
Biaxial Optic Sign
B(-)
add
add
subtract
100 gray + 550 650 blue
100 gray - 550 450 yellow
Biaxial Optic Sign
B(+)
Fig. 11-1A
sub
sub
add
Terima kasih
Top Related