the extracellular protein substance deposited in amyloidosis. It is a waxy, amorphous, eosinophilic, hyalinelike material that exhibits red-green birefringence under polarized light when stained with Congo red.

Amyloid deposits are composed of straight, non-branching fibrils with a diameter of 7.5 to 10 nm and indefinite length. Each fibril is composed of identical polypeptide chains arranged in stacked antiparallel beta-pleated sheets (this is what impar ts the characteristic birefringence under polarized light).