I am using an Internal Standard (hexagonal ZnO) to quantify the amorphous (%) of a glass + metal sample by Rietveld method.

When I have only one crystalline phase + amorphous, I can easily calculate the amorphous (%) using the the follow equation:

A(%) = ((1-(Ws/Rs))/(100-Ws))x10E4, where Ws is the amount of internal standard and Rs is internal standard quantified by Rietveld Method.

But how can I quantify the amorphous (%) when I have TWO crystalline phases + amorphous?

Thank you very much.