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 are called the 'building blocks' of rocks because each rock is 'built' with 2 or more minerals. For example, granite is made of feldspar, quartz, and mica. There are more than 2,700 minerals known today. Hope my answer could be helpful.