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).
Minerals can be the pure element, like Gold, Silver or Copper, but most minerals are compounds of elements, like Quartz (SiO2), and Gypsum CaSO42H2O. The most common mineral then is made up of the two most common elements, Oxygen and Silicon, SiO2. Its a compound of the two elements and its name is Quartz (Silica).