A: According to BBC, an endoskeleton is a bone structure located in the interior of an animal, and an exoskeleton is a bone structure located on the exterior of an animal. Each type of skeleton has unique advantages and disadvantages in helping the animal survive.
Minerals made of only one element are called NATIVE minerals (i.e., silver, gold, mercury, copper). Minerals composed of compounds are simply referred to as minerals (i.e., quartz, which is made up on silicon and oxygen).
An element is a substance made from only one type of atom. For example, Oxygen is an element made up of ONLY oxygen atoms. To understand this better, let us see the how atoms behave. Every element is made up of atoms. Atoms are the smallest piece that can exist in an element.