Abstract
Embryonic halloysites were found in the Ap horizon of a paddy soil derived from volcanic ash. These halloysites were nearly X-ray amorphous to poorly crystallized. They showed infrared absorption bands, more or less poorly defined but characteristic of halloysite, and appeared as “open” spherical to oval particles withdiameters of 15 to 60 nm and as thinly spread “amorphous” materials. About half of halloysites were dissolved incongruently by 0.2M oxalate-oxalic acid (pH3.0) and congruently by hot M/3 sodium citrate. Embryonic halloysites were associatedwith goethite and ferrihydrite containing Al and Si respectively, and abundant diatoms, and considered to form from volcanic ash in a Si-rich environment.
