Corpora amylacea (30-200 μm) are round to oval endogenous concretions arranged in concentric layers; radiating lines may cross the more prominent concentric laminations; they may have a black or birefringent central core; typically pale pink on hematoxylin and eosin (H&E) stain: found in alveoli and alveolar walls; may be surrounded by a rim of macrophages; periodic acid-Schiff (PAS) positive (stain bright magenta); composed of glycoproteins and lack iron and calcium; no known clinical significance but may form around irritating inhaled particles or secretions.