The chemical formula for emerald is Be3Al2SiO36. An emerald can be described asa pure substance because it is a compound.a pure substance because it is an element.an impure substance because it is chemically combined.an impure substance because it is a mixture.

The right answer for the question that is being asked and shown above is that: "a pure substance because it is a compound." The chemical formula for emerald is Be3Al2(SiO3)6. An emerald can be described as a pure substance because it is a compound.