challenge: What is the composition of Ferrohortonolite in terms of fayalite and forsterite?
  
  A. 40% to 60% fayalite and 40% to 60% forsterite
  B. 70% to 90% fayalite and 30% to 10% forsterite
  C. 10% to 30% fayalite and 70% to 90% forsterite
  D. 90% to 100% fayalite and 0% to 10% forsterite
  Answer: 