Westchester County, New York
You are looking down onto the folded surface of a phlogopite sheet.
Phlogopite is a member of the mica family. Micas are like stacks of paper
in that they have a crystal structure formed by sheets of atoms. The
bonds between the sheets are very weak; therefore, the sheets can easily
slide past one another during deformation. Think of the phlogopite as a
crumpled throw rug lying on a smooth floor. Most crumpled rugs have nice
rounded folds, but the folds in this phlogopite are sharp, zigzag kinks.