In our everyday lives, we often find confusion between the terms rock and mineral. People will sometimes use the terms interchangeably since they are both found in the ground. However, they are distinctly different things. Minerals are solids with a definite chemical composition and crystalline structure. While rocks can be made of minerals, and therefore have some of these same properties, they can also be made of materials such as volcanic glass that do not contain a single crystal. The problem is that we do not have a really clear definition of a rock. Different sources will define the term rock in a variety of fashions, with each definition leaving out some outlying versions of rock while including others. For the purposes of this lab, we are going to define rock as any coherent, naturally occurring substance that is usually composed of minerals.