Pyrophyllite in soils from the western amazon region

1. Pyrophyllite in Soils from the Western Amazon Region.
J.J. MARQUES* (Purdue Univ./Univ. Fed. Lavras), D.G. SCHULZE
(Purdue Univ.), W.G. TEIXEIRA (EMBRAPA) and N. CURI (Univ. Fed.
Lavras).
Pyrophyllite is rarely found in soils, but it has been reported in
somesoils from the Amazon region. We studied a soil sequence
from near the Brazil-Peru border consisting of two Fluvents near
the Javari River, one Aquent near an abandoned meander channel,
and two Udults on an adjacent terrace. Smectite and kaolinite
dominate the clay fraction of all the soils. The Fluvents have illite
in all size fractions and chlorite in the coarse clay and fine silt
fractions. The Aquent and Udults have no chlorite, and small
amounts of illite occur only in the coarse clay and fine silt.
Lepidocrocite appears only in the clay fraction of the Aquent.
Pyrophyllite occurs in the fine silt fractions of all of the soils
except one of the Fluvents, and is also present in the coarse clay
of the two Ultisols. Pyrophyllite appears to be inherited from the
parent sediments because it occurs in all the soils, including the
Fluvents. Pyrophyllite appears more resistant to weathering than
chlorite and resistant enough to persist in the Ultisols.
J.J. Marques, (765) 494-8062, jmarques@purdue.edu