Question

Olivine mineral chemical formula is:

• A. \( (\text{Mg}, \text{Fe})_2\text{SiO}_4 \)
• B. \( (\text{Mg}, \text{Fe})_3\text{SiO}_4 \)
• C. \( (\text{Mg}, \text{Fe})_4\text{SiO}_4 \)
• D. \( (\text{Mg}, \text{Fe})_5\text{SiO}_4 \)

Hint:

Olivine = orthosilicate group = \( (\text{Mg}, \text{Fe})_2\text{SiO}_4 \)

Answer 1

The Correct Option is A

To determine the correct chemical formula for olivine, we analyze its mineralogical composition and crystal chemistry.

1. Understanding Olivine Composition:
Olivine is an important rock-forming mineral in the nesosilicate group, commonly found in mafic and ultramafic rocks.

2. Evaluating Each Option:
- (Mg,Fe)₂SiO₄: Correct answer
- (Mg,Fe)₃SiO₄: Incorrect stoichiometry
- (Mg,Fe)₄SiO₄: Incorrect stoichiometry
- (Mg,Fe)₅SiO₄: Incorrect stoichiometry

3. Key Features of Olivine Formula:
- Forms a solid solution series between forsterite (Mg₂SiO₄) and fayalite (Fe₂SiO₄)
- The 2:1:4 ratio of (Mg,Fe):Si:O is fundamental to its orthorhombic crystal structure
- Represents isolated tetrahedral silicate structure (nesosilicate)

4. Crystal Chemical Basis:
- Each SiO₄ tetrahedron is independent
- Divalent cations (Mg²⁺, Fe²⁺) occupy octahedral sites
- Charge balance requires exactly 2 divalent cations per SiO₄ group

5. Why Other Formulas Are Incorrect:
- Higher cation numbers would violate charge balance
- The 2:1:4 ratio is confirmed by X-ray diffraction studies
- All natural olivine analyses fit this formula

Conclusion:
The correct chemical formula for olivine is (Mg,Fe)₂SiO₄.

Final Answer:
The correct option is: (Mg,Fe)₂SiO₄.