Compact bone.
Calcium.
Calcium
Calcium makes them hard.
cancellous bone
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Cortical bone tissue makes up the dense hard outer layer of bone. It is also known as compact bone and provides structure and protection to the inner spongy bone tissue.
By definition all bone is hard. Before bone is fully formed it is made of cartilage and so is softer but it is not called bone at that time in development. Bone is made of hydroxyapetite mainly a calcium and phosphate salt. This makes it hard.
spongy and compact bone
Calcified bones are hard but not really solid. Spongy bone is hard with tiny holes in it. Periosteum is thin but very strong. The other name for it is outer membrane, it helps to rebuild bone cells. The last is cartilage. It is strong material that holds two bones together and allows them to glide over one another. Skull iz also a very strong bone.
The strength and rigidity of the bone is a result of the inorganic salts deposited in the matrix. Matrix is basically just large amount of non-cellular materials, which is what your bones are made of.
bone and hyaline cartilage
Smog.