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).
The mineral silver is a pure element because it is made up of only silver atoms. Most minerals, such as halite and quartz, are made up of chemical compounds. A chemical compound is a substance in which the atoms of two or more elements bond together.