Biotite was altered by boiling in 0.2 M AIC13 solution, and the products were examined by X-ray powder and single-crystal diffraction, chemical analysis and thermogravimetry. The altered material is a 14 A clay mineral with hydroxy-Al interlayers. It has a stacking sequence characteristic 9 of vermiculite and its silicate layers are similar in chemical composition to trioctahedral vermiculite. The results of extracting the interlayer material with sodium citrate sol_ution,' X-ray examinations

more »

... ter heating and thermogravimetry show that the interlayer material is composed of A1 associated with OH and H20. The chemistry and kinetics of the alteration reaction and the orientational betv~een the altered and original biotites are also discussed.