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).
Glass is made of silicon. The only mineral made up exclusively by silicon is quartz, which is also the main mineral in common sand. So the answer is quartz, but you're not wrong thinking sand, only sand is not a mineral.