Why is red phosphorus classified an amorphous solid?

Red Phosphorusis an amorphous polymeric modification of the chemical element

phosphorus. Elemental phosphorus is readily oxidized and this high reactivity results in

hazardous properties of the material. However, red phosphorus is much less reactive and

even more less toxic than yellow (also called white) phosphorus1 (see appendix). Since red

phosphorus is a polymer, an exact molecular formula does not exist. The following

structure serves as an example to illustrate how each phosphorus atom is bonded to three others.

that might help you find something =)