Question

Which is the CORRECT sequence of ore minerals in their increasing order of reflectance?

• A. Galena, Sphalerite, Magnetite, Pyrite
• B. Magnetite, Sphalerite, Galena, Pyrite
• C. Sphalerite, Magnetite, Galena, Pyrite
• D. Galena, Magnetite, Sphalerite, Pyrite

Hint:

To solve reflectance-based sequence questions, recall approximate brightness values under reflected light: sulfides like pyrite are typically much brighter than magnetite and sphalerite.

Answer 1

The Correct Option is C

Step 1: Understanding reflectance.
Reflectance of ore minerals refers to the percentage of incident light reflected from a polished surface under reflected light microscopy. Minerals with higher reflectance appear brighter.

Step 2: Approximate reflectance values.
- Sphalerite: very low reflectance (\(\sim 17%-20%\))
- Magnetite: moderate reflectance (\(\sim 25%-30%\))
- Galena: higher reflectance (\(\sim 43%-45%\))
- Pyrite: highest reflectance among these (\(\sim 55%-57%\))

Step 3: Arrange in increasing order.
From lowest to highest: \[ \text{Sphalerite} < \text{Magnetite} < \text{Galena} < \text{Pyrite} \]

Final Answer: \[ \boxed{\text{(C) Sphalerite, Magnetite, Galena, Pyrite}} \]