Refractometry Flashcards
This is a measure of how effective a material is in bending light coming from a vacuum
Index of Refraction
Most minerals have indices of refraction in the range of _____ to _______
1.4 to 2.0
True or False?
The Index of Refraction is inversely proportional.
True
According to Snell’s Law, the light is refracted ________ the normal upon entering a material with a HIGHER index of refraction.
towards
According to Snell’s Law, the light is refracted ________ from the normal upon entering a material with a LOWER index of refraction.
away
True or False?
Light travels faster if it passes through a material with a high index of refraction
False, light travels slower.
What is the simplest method to measure the Index of Refraction of a Mineral?
Immersion Method
What is the main tool used in the immersion method?
Immersion Oil
This is the degree to which mineral grains stand out from the mounting medium
Relief
A degree of relief observed in mineral grains that are distinct or clear.
High Relief
In HIGH relief, the mineral and oil/balsam indices differ by how much?
0.12 or more
A degree of relief observed in mineral grains that are a bit unclear but still distinguishable.
Moderate Relief
In MODERATE relief, the mineral and oil/balsam indices differ by how much?
0.04 to 0.12
A degree of relief observed in mineral grains that are almost indistinguishable.
Low Relief
In LOW relief, the mineral and oil/balsam indices differ by how much?
0.04
If the index refraction of the oil is EQUAL TO the mineral, what happens to the appearance of the mineral grain?
The Grain does not stand out
If the index refraction of the oil is NOT EQUAL TO the mineral, what happens to the appearance of the mineral grain?
The Grain appears to stand out
True or False?
The relief of anisotropic/birefringent minerals does not change when the stage is rotated.
False, their relief may change.
What is the type of relief when the index of mineral > index of surroundings?
Positive Relief
What is the type of relief when the index of mineral < index of surroundings?
Negative Relief
This is a band of light along the grain boundaries when slightly out of focus
Becke Line
What happens to the Becke Line when the focal distance is increased?
The Becke line goes to the medium with a higher index of refraction.
This is an effect when thinner mineral fragments on the edges act as crude lenses
Lens Effects
This is an effect when the converging light hitting the vertical grain edges is either refracted or internally reflected.
Internal Reflection Effect
What do you call the technique whereby light is projected at the specimen from sideways to reveal features with higher contrast compared to when viewed with brightfield illumination?
Oblique Illumination Method
What is the index refraction of Balsam?
1.540
What is the index refraction of Quartz?
1.544 to 1.553
True or False?
It is possible to get the exact index of refraction of a mineral in a rock with multiple minerals.
False
What is Garnet’s relief?
High Relief
What is the degree of relief of a mineral with a difference in relief from balsam of 0.01?
Low Relief
The velocity of light as it passes through a mineral is compared to the velocity of light in ____________ to get the index of refraction.
Vacuum
A mineral with a lower index of refraction exhibits ______ towards the ________
BRIGHT MARGINS towards the BRIGHT FIELD
True or False?
Light will bend closer to the normal as it passes through a medium of greater refractive index.
True
What is the relief of Quartz?
Low Relief
True or False?
A mineral with a negative relief has an index of refraction less than its surroundings.
True
