Mineralogical Analysis of Clays in Soils Developed from Basalts in Australia

Abstract

Clay mineralogical analyses were made of red soils and black soils developed from southern Victoria, Australia. The clays of the black soils are dominantly montmorillonite (39%) and vermiculite (16%) but have an average siliceous allophane content of 17%. The clays of the red soils are dominantly kaolinite and halloysite (26%) and chlorite (30%) but have an average halloysitic allophane content of 21%. Two to eight per cent of mica and quartz occur in both. A longer period of eolian dust accumulation and concurrent weathering and soil development have occurred in the red soils than in the black soils since the last cycle of geological erosion. A simple chemical method was used for the estimation of allophane (amorphous alumina, silica, and iron oxide with water) and kaolinite plus halloysite. After selective dissolution of allophane, free Al(OH)3, and amorphous SiO2 during 2.5 min of boiling in 0.5N KOH solution, the residue is subjected to heat treatment at 550°C to dehydroxylate the kaolinite and halloysite. This is followed by another 2.5 min dissolution treatment in 0.5N KOH and a further deferration with dithionite. Some iron‐rich montmorillonitesaponite (smectite) and vermiculite are also dehydroxylated on heating and subsequently are partially dissolved in the KOH. The kaolinite and halloysite constituents were then calculated.

Mineralogy and Genesis of Clays in Red‐black Soil Toposequences on Basic Igneous Rocks in Kenya

“…The observation that, e.g. in Australia, black shallow smectitic soils on basalt occur on upper slopes replaced by deep red kaolinitic soils (krasnozems) on lower slopes (Briner and Jackson, 1970) does not contradict this general idea but supports it. The shallow erosional soils represent the initial phase of soil formation which is, as shown above, represented by smectites.…”

Isomorphous Substitution of Iron for Aluminium in Some Soil Kaolinites

“…1). Briner and Jackson (1970) proposed a SiOJR20 3 molar ratio method of calculation to eliminate the interference by other iron-rich phyllosilicates such as partially chloritized montmorillonites which may be dehydroxylated along with kaolinite. El-Attar and Jackson (1973) reported that large quantities of silica and alumina were dissolved from 2:1 layer silicates by the 0.5 N NaOH extraction after dehydroxylation of the clay fractions of montmorillonitic soils in Nile River sediments.…”

Hydrothermal Origin of the Clays from the Upper Slopes of Mauna Kea, Hawaii

“…On the basis of the values of SIO2/A1203 molar ratios, Jackson (1969) differentiated between very siliceous amorphous material with ratios from 2.9 to over 4, siliceous amorphous material with molar ratios of 2.8 to 1.4 and aluminous amorphous material with ratios of 1'1 _4-0.3. These criteria as well as other data available in the literature (Briner and Jackson, 1970;Mokma et ai., 1973), are not strictly applicable in this study since the SiOz/AI203 molar ratio of sample 3-2 (Table 2) was calculated from the elemental analysis rather than from the Na or KOH extract.…”