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).
Diamond is the only gemstone that is made of only one  element, Carbon.   Joseph R. Villarreal, Graduate Gemologist (GIA)   White Fire Diamonds, Inc.    The Correct View   Actually a diamond is an object not an element.he carbon atoms form  layers and the graphite is soft and slippery; which makes it a nice  dry lubricant that is sometimes used in lock cylinders. It's also  opaque; unlike diamond.     Diamond is an element, an allotrope of carbon.