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).
Generally, a mineral is a naturally occurring solid with a crystalline structure. This is where it gets a little tricky. Halite or table salt is a mineral. Sugar is a crystalline solid but comes from plants, sugar cane or sugar beets. This classifies it as an organic compound and so is not a mineral. Coal on the other hand also comes from plants (organic) and is generally considered a mineral.