a mineral is a kind of solid / natural material & if something is made of something / a material then that something contains that something / that material ->  if something is made of minerals then that something contains minerals  if something is made of minerals then that something contains minerals & rock is made of minerals ->  a rock contains minerals  a rock contains minerals & if something contains something else , then that something else will be the component of that something ->  the minerals a rock contains are components of that rock  the minerals a rock contains are components of that rock & something is composed of its components ->  a rock is composed of the minerals it contains  a rock is composed of the minerals it contains & the composition of something can be used to identify that something -> a rock can be identified by the minerals it contains