Differential thermal analysis involves the measurement of heat absorbed or given off by a substance upon heating. The applicability of a portable DTA apparatus on thc clay mineralogical study of alurninous laterites is investigated. Differential thermal curves are presented for a number of laterite samples derived from serpentinite, basalt, and clastic sedimentary rocks.

The standard thermal curves of montmorillonite, halloysite, kaolinite, bauxite. and gibbsite are also discussed, and compared with those obtained from the Surigao laterite. Thermal curves obtained from laterites derived from serpentinite and post-serpentinite sedimentary rocks indicate the presence of bauxite (gibbsite and kaolinite); from basalt and its elastic derivatives show the presence of kaolinite and/or halloysite. Montmorillonite is present in most of the samples studied. Limonite and goethite are known to be present in the laterite section, but the characteristic curves for these minerals are not recorded by the apparatus, except by more sensitive instruments, or the reaction could have been masked by the characteristic dehydration peaks of bauxite and gibbsite in the samples.

Chemical analyses of the samples studied revealed that laterites derived from serpentinite and their elastic derivatives are low in silica, its ratio to alumina is about 1:2, or lower; whereas, those derived from basalt and their clastic derivatives are rich in silica, its ratio to alumina is about 1:1, or higher.

Interpretations drawn from the results of this study are tentative and are subject to moditification by other investigation.