Hyaline cartilage (commonly called "gristle") and bone are the two sclerous
("hard") tissues of the body.
In the early embryo, the skeleton of the limbs is initially formed of hyaline (= "glassy") cartilage which is gradually replaced by the bone except for the ends of bones. Thus, at a joint, articulation is actually between cartilaginous surfaces rather than bony ones.
This is important because cartilage is a far more efficient surface for articulation, being highly resilient and capable of deformation: it is much better able to withstand the forces acting on a joint than bone itself.
cartilage consists of nests of cells (chondrocytes) embedded in a matrix
which is rich in collagen fibres.