Group 1 is the most represented (53% of the total samples) and has a
clay fraction formed by prevailing illite + chlorites, with subordinate interstratified
illite/smectite. Group 2 (20% of the total samples) is entirely
composed of illite, whereas Group 3 (16% of the total samples) is made
up of almost pure smectite (AR7) and interstratified illite/smectite
(AR1). Meanwhile, Groups 4 and 5 correspond to isolated samples
that have a clay fraction composed of kaolinite + illite + smectites
(AR9) and illite + chlorites (AR3), respectively.