The mineral salts are deposited by the osteocytes around the collagen fibers. The inorganic matrix gives the bone hardness. Try soaking a chicken bone in a jar of vinegar for a few days - the minerals will leach out, leaving only the organic matrix. Osteogenesis Bone, like all other connective tissues, is formed from mesenchyme - the embryonic connective tissue. Before you are born this mesenchyme is replaced by the mature connective tissues.
All bones formed via intramembranous ossification are flat bones.
Mesenchymal cells in the center of the membrane differentiate into osteoblasts, which then begin to secrete the organic bone matrix. The osteoblasts then secrete the mineral portion of the matrix. The matrix being formed is called woven bone, an immature bone tissue that will eventually become spongy, or compact bone, depending on the location. Mesenchymal cells form around the ossified portion of the membrane and form a periosteum. The periosteal osteoblasts begin to form bone plates around the spongy bone middle.