[[1]] is a rigid form of connective tissue and is composed principally of calcium.

A bone is a rigid, semi-solid structure that serves as the skeleton of vertebrates, providing support, protection, and movement via muscles attached to the bones. 

Bones are made up of a mineralized matrix, mostly calcium phosphate, and collagen fibres.

They also function as a mineral storage site, such as calcium, and as a blood-forming tissue. Furthermore, bones help to regulate metabolism and hormone production.