Question

A clinopyroxene crystal in a basalt, measured to have a composition of \( \text{Mg}_{1.2} \text{Fe}_{0.4} \text{Ca}_{0.4} \text{Si}_2 \text{O}_6 \), will have an Mg-number (Mg) of............%. (In integer)

Hint:

To calculate the Mg-number (Mg\#), divide the amount of Mg by the sum of Mg and Fe, then multiply by 100 to get the percentage.

Answer 1

Correct Answer: 75

The Mg-number (Mg\#) is calculated using the formula: 
\[ \text{Mg\#} = \frac{\text{Mg}}{\text{Mg} + \text{Fe}} \times 100 \]
Step 1: 
The amount of Mg in the formula is 1.2, and the amount of Fe is 0.4.

Step 2: Substitute the values into the formula:
\[ \text{Mg\#} = \frac{1.2}{1.2 + 0.4} \times 100 = \frac{1.2}{1.6} \times 100 \]

Step 3: Calculate the Mg\#:
\[ \text{Mg\#} = 0.75 \times 100 = 75 % \]
Thus, the Mg number (Mg) is 75%. 
\[ \boxed{75} \]