T hundereggs look like regular rocks from the outside, but contain intricate and colorful mineral patterns inside — often made of quartz, chalcedony, or agate. They are nodule-like rocks ...

Pure quartz, or “rock crystal” from Brazil. Source: Didier Descouens, CC BY-SA 4.0 Pick up a rock almost anywhere on Earth and chances are pretty good that there’s at least some quartz in it.

This process could explain why large gold nuggets are so often associated with quartz veins found in tectonically active areas or even rocks shattered by earthquakes. “In essence, the quartz ...