Mast cells, so-called tissue basophils, are not a component of granulopoiesis, but rather belong to the bone marrow stroma. They are usually found in the bone marrow spicules. They are distinct from the basophils of bone marrow.
The basophilic granules are densely packed, thereby causing the cell to appear as a dark violet dot in low magnification. The round nucleus is only partially covered by the granules and is seen as a halo in the center.