GLY 3202C - Exam 2 (Module 4-6) Questions and Answers
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GLY 3202C
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GLY 3202C
A mineral is black under plane polarized light and stays black on rotation under crosspolarized light. How would you classify it? - ️️Opaque
When the accessory plate is inserted, what happens to the upper right (NE) quadrant,
just inside the isogyre, of a uniaxial or biaxial interference figu...
GLY 3202C - Exam 2 (Module 4-6)
A mineral is black under plane polarized light and stays black on rotation under cross-
polarized light. How would you classify it? - ✔️✔️Opaque
When the accessory plate is inserted, what happens to the upper right (NE) quadrant,
just inside the isogyre, of a uniaxial or biaxial interference figure for a mineral with a
negative optic sign? - ✔️✔️It turns yellow
True or false? Rocks must be sliced into thin sections in order to be viewed under the
petrographic microscope. - ✔️✔️True
What is refraction? - ✔️✔️When light bends as it crosses a boundary between two
mediums.
Which mineral has the lowest relief relative to epoxy resin (n=1.537)? (n is approximate)
- ✔️✔️Quartz: n=1.5
Which property of a light wave determines its color? - ✔️✔️Wavelength
What is defined as the difference between the maximum and minimum refractive indices
for a crystal? - ✔️✔️Birefringence
How does light vibrate when it has traveled from the light source and through the lower
polarizer? - ✔️✔️Light vibrates in a single plane.
Is amorphous material such as basaltic glass isotropic of anisotropic? - ✔️✔️Isotropic
What property is defined as a crystal changing color on rotation under plane polarized
light? - ✔️✔️Pleochroism
Which lighting condition(s) would you use to observe extinction? - ✔️✔️Cross-polarized
light
Which crystal system(s) will look extinct when observed directly down the c-axis?
[Select all that apply.] - ✔️✔️Hexagonal
Tetragonal
What does the 2V angle measure? - ✔️✔️The angle between two optic axes.
, You observe a crystal with strong pleochroism in PPL. Which mineral(s) could it be?
[Select all that apply.] - ✔️✔️Hornblende
Biotite
Which property would distinguish between quartz and garnet? - ✔️✔️Relief
In which mineral does light travel the slowest? (n is approximate) - ✔️✔️Garnet: n=1.9
Which lighting condition is produced when only the lower polarizer is inserted? -
✔️✔️Plane polarized light
Given that calcite has refractive indices of 1.66 perpendicular to the c-axis, and 1.49
parallel to the c-axis - what is the maximum birefringence? - ✔️✔️0.17
If a mineral has the same refractive index in all crystallographic directions is it isotropic
or anisotropic? - ✔️✔️Isotropic
What is retardation? - ✔️✔️Retardation is the distance that the slow ray lags behind
the fast ray.
A mineral goes black every 90° on rotation under cross-polarized light and is
transparent in plane polarized light. How would you classify it? - ✔️✔️Anisotropic
True or false? A crystal will display the same optical properties, such as interference
color, regardless of the orientation of the crystal within the thin section. - ✔️✔️False
Which crystal system(s) is(are) biaxial? [Select all that apply.] - ✔️✔️Orthorhombic
Triclinic
Monoclinic
Which optical classification of minerals is defined as minerals where light entering in all
but one special direction is split into two rays? - ✔️✔️Uniaxial
Which crystal system(s) will show interference colors when observed directly down the
c-axis? [Select all that apply.] - ✔️✔️Monoclinic
Orthorhombic
Triclinic
What is an optic axis? - ✔️✔️A direction through an anisotropic crystal along which
light rays do not split.
Where is the optic axis on a uniaxial optic axis interference figure? - ✔️✔️A point in the
center of the figure.
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