Relationships between composition and structure in Fe-rich smectites

Abstract

Chemical and crystallochemical properties of natural dioctahedral Fe-rich smectites formed by weathering of basaltic rocks in the Berici-Euganei Area, northern Italy, were investigated. It was found that: (i) the b-dimension could be correlated both to Fe³⁺/Σ ratio (Σ = octahedral occupancy) and to dehydroxylation peak temperature in the range 400–600°C; (ii) it is not correct to impose a total octahedral occupancy strictly equal to 2 for dioctahedral smectites; (iii) in the smectite group there is not a continuous isomorphous series as would appear on the basis of chemical features only.