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).
A: A material that contains only one type of atom is called an element. There are 98 elements known to occur naturally, along with another 20 that have been synthesized in laboratories, as of 2015. Hydrogen, the lightest element, is also the most abundant chemical substance in the universe.