Abstract--Hydroxy-Al and -Fe interlayers were prepared in "mono-mineralic" fine and coarse clay montmorillonite and coarse clay and silt vermiculite at 3~ and 21~ The formation of hydroxy interlayers was evaluated by X-ray diffraction, cation exchange capacity, and chemical analyses.At comparable particle size and regardless of temperature, the amounts of hydroxy-Al and -Fe interlayers in montmorillonite exceeded by far those formed in vermiculite. Likewise, the aluminum systems exhibited a higher degree of interlayering than iron systems.Within montmorillonite, the amount of hydroxy-A1 and -Fe interlayers increased as the particle size decreased, regardless of temperature. The aluminum interlayered montmorillonite equilibrated at 3~ was characterized by basal spacings of about 17 ,~ after Ca-saturation plus 54 per cent relative humidity. These spacings are larger than those normally observed for smectites.Within vermiculite systems equilibrated at 3~ more hydroxy-AI interlayers were recorded in coarse clay than in silt fraction, whereas at 2 I~ about equal amounts of interlayers were formed. By contrast, hydroxy-Fe interlayer was favored by the silt fraction at both temperature levels.The formation of aluminum interlayers in both minerals increased with increasing temperature. The formation of hydroxy-Fe interlayers in montmorillonite was generally not temperature dependent, whereas the formation of such interlayers in vermiculite increased slightly with increasing temperature.These data may partially explain the formation of chloritic intergrades in soils as a function of type of minerals, kind of ions, and thermal variations.

Hydroxy‐Al and ‐Fe interlayers were formed in montmorillonite and vermiculite by adding AlCl3 or FeCl3 and NaOH in amounts to give a wide range of pH. The resulting chloritic intergrades were examined aften 10 days, 6 months, and 1 year.Aluminum‐interlayered montmorillonite formed at pH 4.6 after 10 days showed the essential X‐ray characteristics of chlorite. The best iron interlayers in montmorillonite prevented collapse upon K‐saturation and heating but did not prevent expansion upon solvation. Aluminum‐interlayered vermiculite showed partial collapse on K‐saturation and heating.Acid conditions favored interlayer formation with aluminum and iron in montmorillonite and with aluminum in vermiculite. Iron interlayers in vermiculite were favored by alkaline conditions.Iron interlayers decreased with time. Aluminum interlayers formed in montmorillonite with acid conditions decreased sharply with time. Aluminum interlayers in vermiculite and those formed under alkaline conditions in montmorillonite, showed some tendency to increase with time.

Abstract-A study was conducted to (1) determine the conditions of hydroxy-Mg interlayer formation with respect to type of clay mineral, acidity, and time; (2) evaluate the stability of this interlayer to dissolution treatments; and (3) ascertain the effects of such treatments upon the determination of clay minerals in soils and sediments. Hydroxy-Mg interlayers were formed in montmorillonite and vermiculite by adding MgCI~ and NaOH in amounts to give a wide range of pH. The resulting chloritic intergrades were examined after 10 days, 6 months, and 1 yr.Alkaline conditions favored the formation of hydroxy magnesium interlayers in phyllosilicates. Hydroxy-Mg interlayered montmoriUonite which resulted from 10 days equilibration at pH 10.4 did not expand upon solvation with ethylene glycol and exhibited practically no collapse after K-saturation and heating at 550~ A small amount of interlayer was formed between pH 6.8 and 9.8 (10 days). In contrast, vermiculite exhibited no evidence of interlayer formation at pH values up to 9-7 (10 days). Chloritic intergrades formed at pH 10-7 did not collapse after K-saturation and heating at 300~ but did so at 550~ Hydroxy-Mg interlayers were not formed in either mineral by using a drying method. This method apparently failed to provide the required alkaline conditions for interlayer formation.The amount of magnesium interlayers present in the phyllosilicate systems decreased with time. The interlayers formed in vermiculite decreased more sharply than those in montmorillonite.Sequential dissolution treatments included boiling 2 per cent Na~CO3, buffered sodium citratedithionite, a second citrate-dithionite treatment, and boiling NaOH. Hydroxy-Mg interlayers in montmorillonite exhibited a higher stability to sequential treatments than the interlayers formed in vermiculite. A stable 14 ,~ line was observed in interlayered montmorillonite after the dithionitecitrate and NaOH treatments.The interlayers in montmorillonite showed a relatively high stability to HCI dissolution treatments. In contrast, most of the magnesium interlayer in vermiculite was removed by two HC1 washings.The reagents used in this study are sometimes used to remove coatings and cementing agents from soil surfaces prior to particle size and clay analysis. The present data show that these treatments also remove some hydroxy-Mg interlayers and produce changes in properties of clays, A proper interpretation of data for clay mineral identification and characterization must recognize these changes due to treatment.