* Organic material (about 30%): This includes:

* Collagen: A protein that provides flexibility and tensile strength.

* Other proteins: Such as osteocalcin, osteopontin, and bone sialoprotein.

* Inorganic material (about 70%): This includes:

* Hydroxyapatite: A mineral that gives bones their hardness and rigidity. This is primarily composed of calcium and phosphate.

In addition to these main components, bones also contain small amounts of water and other trace elements.

The ratio of organic to inorganic material changes with age. Younger bones have a higher proportion of organic material, making them more flexible, while older bones have a higher proportion of inorganic material, making them more brittle.