CHANGES IN PARTICLE MORPHOLOGY DURING ILLITIZATION - AN EXPERIMENTAL-STUDY

Smectite was reacted at several temperatures between 20-degrees-C and 500-degrees-C to produce interstratified illite/smectite (I/S) with di fferent proportions of expandable layers. Dispersed and sedimented pro ducts were examined using a transmission electron microscope. Particle size and aspect ratio showed no systematic change as a function of re action extent during RO illitization. However, particles exhibited rou nded edges during the early stages of the reaction, suggesting some di ssolution of primary smectite. Additionally, increasing particle contr ast in the electron beam suggests thickening of particles with increas ing reaction extent. The thickening of particles is thought to be prod uced by the nucleation and precipitation of secondary illite layers on primary smectite layers. In the most extensively reacted I/S, particl es have become aggregated into clumps or quasicrystals by lateral grow th of illite layers. Internal uniformity of crystallographic alignment of individual growing crystals within each aggregate was reflected in the increasing frequency of 60-degrees and 120-degrees interfacial an gles within each aggregate. In highly illitic I/S, these aggregates to ok on an overall euhedral form and became crystallographically contigu ous, producing single crystal electron diffraction patterns.