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).
Most rocks are made from more than one mineral, but there are quite a few kinds that are made from only one mineral. Minerals are not rocks, rocks are made of minerals. A car is made of steel, glass, and plastic. A rock is like the car, a mineral is like the steel, or glass, or plastic.