The integrated absorbance (total area under the curve in the OH region) can be related to the H₂O content of the garnet.
 
 

Infrared spectrum of synthetic katoite	The grossular calibration

We can ask the following question:  'Does this calibration line applies to low concentrations of OH in the nominally anhydrous minerals?'
 

Reference:  Rossman GR, Aines RD (1991) The hydrous components in garnets: grossular - hydrogrossular. American Mineralogist 76, 1153-1164.