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 have a definite chemical composition. Each one is made of a particular mix of chemical elements. Minerals have an ordered atomic arrangement. The chemical elements that make up each mineral are arranged in a particular way - this is why minerals 'grow' as crystals.