Publication: On the chemical composition of sepiolite and palygorskite
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Publication Date
2010
Authors
SĂșarez Barrios, Mercedes
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Clay Minerals Society
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Abstract
Many studies of the chemical composition of sepiolite and palygorskite have been carried out
using analytical electron microscopy (AEM). According to the literature, a compositional gap exists
between sepiolites and palygorskites, but the results presented here show that they may all be intermediate
compositions between two extremes. The results of >1000 AEM analyses and structural formulae have
been obtained for the samples studied (22 samples of sepiolite and 21 samples of palygorskite) and indicate
that no compositional gap exists between sepiolite and palygorskite. Sepiolite occupies the most magnesic
and trioctahedral extreme and palygorskite the most aluminic-magnesic and dioctahedral extreme.
Sepiolite and palygorskite with intermediate compositions exist between the two pure extremes:
(1) sepiolite with a small proportion of octahedral substitution; (2) palygorskite with a very wide range of
substitution (the pure dioctahedral extreme is unusual); and (3) intermediate forms, Al-sepiolite and Mgpalygorskite
with similar or the same chemical composition. The chemical compositions of the
intermediate forms can be so similar that a certain degree of polymorphism exists between Al-sepiolite and
Mg-palygorskite.