_______ makes up 14 to 17 percent of the human skeleton.

  The human skeleton is composed largely of a mineralized matrix called hydroxyapatite, which imparts bones their hard, rigid properties. On a weight basis, phosphorus is the second most abundant mineral in the human body. About 85% of the total phosphorus in the body is found in bones and teeth. If we consider bone minerals as a whole, phosphorus is usually about 14% to 17% of bone minerals. Calcium takes the lead as the most abundant mineral in the bone, contributing about 39% to bone minerals. However, there are other minerals as well, although in much smaller proportions. Magnesium, sodium, and iron are present only in trace amounts. For example, magnesium contributes less than 1% to bone ash.