Without a regular structure. Amorphous minerals do not have a repeating crystalline matrix. Glass, for example, is amorphous because it is cooled in the kiln quickly enough that no crystals have an opportunity to form.
Glass vs. Crystalline
In ceramics, understanding the difference between what a glass and crystal are provides the basis for understanding the physical presence of glazes and clay bodies.
Ceramic glazes form crystals on cooling if the chemistry is right and the rate of cool is slow enough to permit molecular movement to the preferred orientation.