Question

Which of the following property/properties of a mineral indicate(s) uniaxial negative optic sign?

• A. Ordinary ray is slow
• B. Extraordinary ray is slow
• C. \(n_e<n_o\)
• D. \(n_e>n_o\)

Hint:

For uniaxial negative minerals, remember that \(n_e<n_o\), which means the extraordinary ray has a lower refractive index than the ordinary ray.

Answer 1

The Correct Option is C

Step 1: Understanding the Uniaxial Negative Optic Sign.
In mineralogy, the optic sign of a uniaxial mineral refers to how the refractive indices for light traveling in different directions are related. For a uniaxial negative mineral, the refractive index of the extraordinary ray (\(n_e\)) is less than the refractive index of the ordinary ray (\(n_o\)).
Step 2: Analyzing the Options.
- Option (A): The ordinary ray is slow, but this is not a specific indicator of the optic sign.
- Option (B): The extraordinary ray being slow is a feature of uniaxial positive minerals, not negative.
- Option (C): The condition \(n_e<n_o\) is the defining characteristic of uniaxial negative minerals.
- Option (D): \(n_e>n_o\) is the condition for uniaxial positive minerals.
Thus, the correct answer is (C) \(n_e<n_o\).
Final Answer: \[ \boxed{n_e<n_o} \]