Conoscopic Observation Flashcards
Involves an unfocused light beam that travels from the substage, through the thin section, and straight up the microscope tube to the ocular lens and our eyes.
The light rays travel perpendicular to the stage and perpendicular to a thin section on the stage.
Orthoscopic View
the mineral is viewed simultaneously from different angles in a cone of light using the maximum aperture
Condenser engaged to focus on a small spot on the sample.
Bertrand(-Amici) lens engaged for light to again
travel vertically before it reaches the ocular.
Conoscopic View
_______ _______ is used to:
To get interference figures.
To determine whether an anisotropic mineral is
uniaxial or biaxial.
To determine if a mineral is optically positive or
negative.
To determine 2V angle of biaxial minerals.
Conoscopic View
Corresponds to the direction of emergence of the optic axis.
Melatope
Dark bands that make up the cross.
Isogyre
Bands of equal light retardation / birefringence.
Isochrome
Interference Figures:
ε or ε’
Vibrates Radially
Interference Figures:
ωITTI
ω (Extraordinary Ray) is tangent to isochrome
Optically positive minerals: nε > nω; Extraordinary Rays = _______ _______
Slow Rays
Optically negative minerals: nω > nε; extraordinary rays = _______ _______
Fast Rays
Optic Sign and Characterization of Ordinary Rays in Prolate Spheroids.
Optically Positive, Slow Rays
Optic Sign and Characterization of Ordinary Rays in Oblate Spheroids.
Optically Negative, Fast Rays
True or False:
If a minerals has a high birefringence, it means that their isochromes are more visible and clear.
True
If NE and SW quadrants increase orders, addition of retardation has occurred > εʹ is the slow ray > crystal is _______ _______.
Uniaxial Positive
If NW and SE quadrants increase orders, subtraction of retardation has occurred > εʹ is the fast ray > crystal is _______ _______.
Uniaxial Negative
In uniaxial minerals, when the yellows are in the 2nd and 4th quadrants, and the blues are in the 1st and 3rd quadrants, the optic sign of the mineral is _______ _______.
Uniaxial Positive
In uniaxial minerals, when the blues are in the 2nd and 4th quadrants, and the yellows are in the 1st and 3rd quadrants, the optic sign of the mineral is _______ _______.
Uniaxial Negative
The acute angles between the two Optic Axes.
2V Angle
True or False:
When viewing the isogyres of biaxial minerals, the isogyres forms a cross.
False, the isogyres are generally diffused, separating to form two arched lines or a single straight line.
If the 2V angle is 0 degrees, you can classify the mineral as?
Uniaxial
If the isogyre forms a straight line, the 2V angle is ___ degrees.
90
The line bisecting the acute angle between the two optic axes.
Acute Bisectrix (Bxa)
The line bisecting the obtuse angle between the two optic axes.
Obtuse Bisectrix (Bxo)
If viewed in Bxa:
Corresponds to the view along the z-axis.
Biaxial Positive
If viewed in Bxa:
Corresponds to the view along the x-axis.
Biaxial Negative
If viewed in Bxo:
Corresponds to the view along the x-axis.
Biaxial Positive
If viewed in Bxo:
Corresponds to the view along the z-axis.
Biaxial Negative
Normal to the plane of the two optic axes.
Optic Normal (ON) Figure
If the Bxa view is parallel to the fast direction, the optic sign of the mineral is?
Biaxial Negative
If the Bxa view is parallel to the slow direction, the optic sign of the mineral is?
Biaxial Positive
When assigning the optic sign of Biaxial Minerals, if the blues are in the 2V angle, outside the curves of the isogyre, and the yellows are inside the curve of the isogyre, the sign is?
Biaxial Negative
When assigning the optic sign of Biaxial Minerals, if the yellows are in the 2V angle, outside the isogyre curves, and the blues are inside the curve of the isogyre, the sign is?
Biaxial Positive
Part of the view that corresponds to the areas of extinction of a crystal.
Isogyre
If there is an increase in birefringence in quadrants I and III, the optic sign of a mineral is uniaxial/biaxial __________.
Positive
The less curved the arc of the isogyre is, the ________ the 2V angle.
Larger
Which of the following is not necessary to view interference figures?
A. Bertrand-Amici lens
B. Condenser
C. Analyser
D. Compensator
D. Compensator
We get a flash figure if the optic axis lies _________ to the microscope stage
Parallel
The _______ plate corresponds to one full retardation, i.e. ~500nm.
Gypsum
True or False:
Only uniaxial minerals with high birefringence have isochromes.
False
Conoscopic analysis is best viewed in _________ magnification.
High
