Light micrograph of thyroid tissue containing calcium oxalate crystals (the clear-yellowish irregular shaped structures within the pink areas). Calcium oxalate crystals are normally present in the thyroid, which can help a pathologist identify this organ and distinguish it from parathyroid tissue which may otherwise look similar. The crystals are present within thyroid follicles, which are the large roughly round structures filled with pink staining colloid substance. Haematoxylin and eosin stained tissue section. Magnification: 100x when printed at 10 cm.