Dear Mr. Morad,

such chemical indices are attractive to those who do not know the side effects and cast aside other processes leading to similar datasets. The ratios pretend to be all-embracing if you ignore the "small print". In my opinion they should be used with a stark warning and always supported by other methods from different geoscientic disciplines such as geology, mineralogy and shallow geophysics.

Best regards

H.G.Dill

Hi Ahmed Morad:

Agree with Prof Dill on the application of CIA to evaluating geological processes. Definitely, the CIA is useful although more petrographic observations are needed to aid your interpretation.

Best regards,

Xue-Ming Yang

Thanks everyone I learnt alot from your answers. :)

Simply, you can not distinguish between the chemical changes brought by metamorphism or weathering by using CIA. CIA will give composite picture of alteration irrespective of pre and post depositional processes.