Question

The core-rim compositions of a normally zoned plagioclase crystal are as follows:
Core: Ca₀.₆Na₀.₄Al₁.₆Si₂.₄O₈
Rim: Ca₀.₄Na₀.₆Al₁.₄Si₂.₆O₈
The amount of increase of Na atom from core to rim per formula unit of plagioclase is (give answer in one decimal place).

Hint:

The increase in cation concentration can be calculated by subtracting the core value from the rim value.

Answer 1

Step 1: Understanding the question.
The question asks for the increase in the amount of Na atom from core to rim per formula unit of plagioclase crystal.
Step 2: Analyzing the solution.
The Na content in the core is 0.4 and in the rim is 0.6. The increase in Na is: \[ \text{Increase in Na} = 0.6 - 0.4 = 0.2 \] Step 3: Conclusion.
The correct answer is 0.2, which is the increase in Na atom from core to rim per formula unit.