pressure at which the processes occurred temperature at which the processes occurred chemical impurities present as the processes occurred amount of time passed since the processes occurred
I gave my students this multiple choice question: The mineral quartz naturally forms in various colors. Which difference in quartz formation results in the different colors?

Only one answer is correct among these 4 choices:
- pressure at which the processes occurred
- temperature at which the processes occurred
- chemical impurities present as the processes occurred
- amount of time passed since the processes occurred

Could you tell me which one is correct?

chemical impurities present as the processes occurred