Figure 2. Osteoblasts and Osteoid Tissue. A: Light micrograph of a group of osteoblasts producing osteoid; note the newly embedded osteocyte. B: Electron micrograph of 3 osteoblasts covering a layer of mineralizing osteoid tissue. Note the prominent Golgi and endoplasmic reticulum characteristic of active osteoblasts. The black clusters in the osteoid tissue are deposits of mineral. C: Osteoblast Lineage. Osteoblasts originate from undifferentiated mesenchymal cells which are capable of proliferation and which may differentiate into one of a range of cell types. The preosteoblast is also capable of proliferation and may be already commited to an osteoblast phenotype. The mature osteoblast no longer proliferates, but can differentiate further into an osteocyte once embedded in the bone matrix, or to a lining cell on the bone surface.