Platelets are membrane bound bits of megakaryocyte cytoplasm, measuring only 1-4 microns in diameter. They are the smallest of the formed elements found in normal peripheral blood. The arrows point to platelets.
Their shape varies greatly, but they are usually round, oval, or rod-shaped. Platelets stain light blue to purple and are very granular.
The cytoplasm of platelets can be divided into two areas: the chromomere and the hyalomere. The chromomere is located centrally where the granules tend to aggregate. The hyalomere surrounds the chromomere and is a clear, blue, non-granular zone. The lower image on the right illustrates the central granular chromomere, and the peripheral clear hyalomere of a platelet.