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).
Some of the most abundant minerals found on the crust include quartz, hematite and orthoclase. Quartz is composed of silicon and oxygen; hematite is made up of iron and oxygen; and orthoclase is a potassium aluminum silicate compound. The chemical combination of one or more minerals produce rocks. The general elemental composition of rocks mainly include silicon, oxygen, aluminum, calcium, potassium and sodium.