Swelling minerals in a basalt and its weathering products from Morvern, Scotland: I. Interstratified montmorillonite-vermiculite-illite

Abstract

The main clay mineral in weathered basaltic rubble has been shown by X-ray diffraction, chemical, infrared and differential thermal methods to be an interstratification of montmorillonite, vermiculite and illite in the approximate ratio 2:1:1, the montmorillonite having some degree of segregation and the vermiculite and illite being randomly interstratified. All three components are dioctahedral, the swelling ones having a high tetrahedral charge, a large aluminium content, and very little iron. Despite the 50% montmorillonite content of the mineral, its infrared absorption pattern is generally illitic in character.