Soil Kaolinite, Vermiculite, and Chlorite Identification by an Improved Lithium DMSO X-ray Diffraction Test

The thermal treatment of K-saturated soil clays does not reliably differentiate between kaolinite and chlorite by the 7Å XRD peak loss. Dimethylsulfoxide (DMSO) treatment for expansion of soil kaolinites to 11.2Å is effective in expanding the vermiculite 14Å peak from that of chlorite by Li, H₂O, time, and temperature control in a group of kaolinite-rich soils (Eau Pleine, Marathon, Rietbrock, Dolph, and Kert series, all from Marathon and Wood Counties) from central Wisconsin. Only partial expansion of soil vermiculite to 18.8Å occurs when the sample is Na⁺-saturated, but expansion is complete with Li⁺ saturation after the sample has been allowed to stand in a dilute (<0.01N) LiCl solution. The intercalation of expansible clays by DMSO is optimum only when the liquid contains H₂O, but <10% H₂O, and the clay is allowed to stand in the DMSO-H₂O-LiCl at 90°C overnight. A 50-mg sample of clay in a 15-ml plastic centrifuge tube is washed twice with 5 ml 1N LiCl and once with 4 ml 0.1N LiCl ml⁻¹ cake (paste) volume, the suspension in this third washing being allowed to stand for 2 hours at 50°C to promote flocculation before centrifugation. The sample is washed twice with 9 ml of DMSO ml⁻¹ of cake volume, the suspension in the second washing (>90% DMSO, <10% H₂O solution of <0.01N LiCl) being allowed to stand overnight at 90°C. The tube is centrifuged and 70° of the supernatant is discarded. The remaining sample is stirred, spread on a porous, dry ceramic tile to dry partially by imbibition, and X-rayed while still moist to prevent the collapse of the vermiculite- and montmorillonite-DMSO 18.8Å complexes. The diagnostic X-ray diffractogram peaks are: kaolinite, 11.2Å; vermiculite and montmorillonite, 18.8Å; chlorite, 7.2 and 14.4Å; mica, 10Å. Intergrade chlorite-vermiculite mainly remains at 14.4Å; mixed-layer systems remain mixed-layered, according to the component minerals present.