challenge: What is the general composition of amphibole minerals?
  
  A. Single chain SiO4 tetrahedra, linked at the edges and containing ions of calcium and potassium
  B. Triple chain SiO4 tetrahedra, linked at the faces and containing ions of sodium and aluminum
  C. Double chain SiO4 tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium
  D. Quadruple chain SiO4 tetrahedra, linked at the corners and containing ions of copper and zinc
  Answer: 