Emerald ore

• Emerald ore
  Locality: Columbia
  
  Among beryl, the green ones are called emeralds, and they contain silicate, oxygen, beryllium, and aluminum.
  Emerald crystal is hexagonal system, and it is colored green because trace amount of chromium (or vanadium) substitute for certain aluminum
  If iron substitutes instead of chromium (or vanadium), the mineral would be aquamarine.