Clay Minerals Ratio
"The clay ratio is a ratio of the SWIR1 and SWIR2 bands. This ratio leverages the fact that hydrous minerals such as the clays, alunite absorb radiation in the 2.0–2.3 micron portion of the spectrum. This index mitigates illumination changes due to terrain since it is a ratio.
Clay Minerals Ratio = SWIR1 / SWIR2
SWIR1 = pixel values from the short-wave infrared 1 band
SWIR2 = pixel values from the short-wave infrared 2 band
Reference: Amro F. Alasta, "Using Remote Sensing data to identify iron deposits in central western Libya." International Conference on Emerging Trends in Computer and Image Processing (ICETCIP'2011) Bangkok Dec., 2011." (ESRI, 2018)