The Internal Geometry of Crystals: Feynman's Physics Explained

Feynman Vol II10-11

Most solids are crystals: their atoms sit in a regular, repeating three-dimensional lattice. That hidden geometric order is responsible for a crystal's outward shape, its clean cleavage planes, and the fact that properties like conductivity or refractive index can differ along different directions. Studying these symmetries is the science of crystallography.

The big idea

A crystal's outer shape echoes the hidden order of its atoms.

Think about it

Why do salt crystals always break into neat little cubes rather than random shapes?

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