The crystals themselves are fractal: their microscopic and macroscopic forms are similar.

Crystals are formed by repeatedly adding the the same primitive elements in the same way.

" Definition of Fractal

A word coined by Benoit Mandelbrot in 1975 to describe shapes that are "self-similar" -- that is, shapes that look the same at different magnifications. To create a fractal, you start with a simple shape and duplicate it successively according to a set of fixed rules. Oddly enough, such a simple formula for creating shapes can produce very complex structures, some of which have a striking resemblance to objects that appear in the real world. For example, graphics designers use fractals to generate images of mountainous landscapes, coastlines, and flowers.

"http://www.angelfire.com/anime3/internet/graphics.htm