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