Question

The ratio of silicon to oxygen in pyroxenes is:

• A. 1:1
• B. 1:2
• C. 3:1
• D. 1:3

Hint:

Pyroxenes = single chain silicates = Si:O ratio = 1:3.

Answer 1

The Correct Option is D

To determine the correct silicon-to-oxygen ratio in pyroxenes, let's analyze their chemical structure:

1. Pyroxene Structure:
Pyroxenes are single-chain silicates with the general formula: 

XY(Si₂O₆)
where:

• X = Ca²⁺, Na⁺, Mg²⁺, Fe²⁺
• Y = Mg²⁺, Fe²⁺, Fe³⁺, Al³⁺

2. Silicon-Oxygen Ratio Calculation:
The (Si₂O₆)^4- unit shows:

• 2 silicon (Si) atoms
• 6 oxygen (O) atoms

Thus, the Si:O ratio = 2:6 = 1:3

3. Why Other Ratios Are Incorrect:
- 1:1 would require SiO (doesn't exist in silicates)
- 1:2 is the ratio in feldspars and quartz
- 3:1 is impossible as oxygen always exceeds silicon

Final Answer:
The correct ratio is 1:3.