Petrography Final

What is a typical extinction angle for orthopyroxene?

• 0 degrees

• 15 degrees

To find the birefringence (δ) of a mineral, look for a mineral grain with the:

• Lowest possible interference color

• Highest possible interference color

What is the range of wavelengths of radiation that humans can see?

• 400 to 800 nm

• 400 to 800 Å

The refractive index(s) of a mineral can depend on the direction of light.

• is the ratio of speed of light in a vacuum to the speed of light in the mineral

• can depend on direction of light

• are used to determine birefringence

• all of the above

What is the thickness of a standard thin section?

• 0.03 mm

• 3x10-10 m.

Biaxial minerals have

• 2 optic axes and 2 indices of refraction

• 3 optic axes and 2 indices of refraction

• 2 optic axes and 3 indices of refraction

An isotropic mineral:

• Has no birefringence

• Has no relief

Plane-polarized light, upon entering anisotropic minerals

• Splits into two vibrations at right angles to each other with identical velocities

• Splits into two vibrations at right angles to each other with different velocities

• is reflected according to snells law

In PPL, a mineral changes its color when rotated. This is called:

• Birefringence

• pleochroism

A mineral with a refractive index of 1.7 mounted in epoxy with a refractive index of 1.55 will show:

• high positive relief

• low relief