I love thinking about the magnificent forces behind how mountains are formed, how the ocean floor has its own sets of mountains, and how rivers are carved. Geological history makes me feel like I'm part of something so much bigger, and reminds me that I have responsibility for the habitability of our planet in both the near and very, very distant future.

Geology is biological destiny: Whatever minerals land or are deposited in a place determine what or who can make a living there millions of years later.

Alas, their magnificence is not permanent. Amethyst, which is a form of quartz, is typically yellow or gray, Dr. Harlow informed me. The purple was a result of radiation damage, probably from the surrounding rocks in which the amethysts formed, and would most likely revert to its original color eventually. Not even stones are immortal.