THE PHYSICAL, CHEMICAL, AND MINERAL0G1CAL PROPERTIES OF LATERITE SAMPLES FORMED IN VARIOUS ENVIRONMENTS

THE PHYSICAL, CHEMICAL, AND MINERAL0G1CAL PROPERTIES OF LATERITE SAMPLES FORMED IN VARIOUS ENVIRONMENTS

Abstract:

The Physical, Chemical, and Mineralogical Properties of Laterite Samples Formed in Various Environments. (Under the direction of STANLEY W. BUOL). Samples of l a t e r i t e were obtained from Australia, Bolivia, B r a z i l, Nigeria, Thailand, and the U. S. A. The l a t e r i t e materials were found to have a yery wide range of chemical and morphological characteristics. A prominent feature of all samples is a high content of iron and/or aluminum, r e l a t i v e to other constituents. The amount of free iron varies from 4.7 to 44.6% on an oxide basis. Iron is present in the form of goet h i t e , hematite, lepidocrocite, as poorly c r y s t a l l i n e oxide compounds, and as unidentified coatings on other minerals. The other minerals i d e n t i f i ed in the l a t e r i t e samples were kaolin minerals, which are common in a l l samples, quartz, feldspars, and micas. Quartz is an i n e r t component and is believed to be derived from the underlying acidic rocks. The structure of l a t e r i t e as observed in thin sections and with the scanning electron microscope is complex and displays an even greater variety than the chemical composition. One structural extreme is the type composed largely of p i s o l i t i c bodies more or less closely packed in a matrix. The other extreme of structure is the vesicular type in which the cavities are either empty, f i l l e d or partly f i l l e d with clay minerals. In addition, data obtained indicate a strong relationship between color and iron mineralogy. The reddish colored samples have a high content of hematite while the yellowish samples have a high goethite content. Also, samples with a low active iron r a t i o tend to have a reddish color while those with a high active iron r a t i o are yellowish in color. Another relationship detected shows that samples that have a high content of kaol i n i t e (- 60%) are dominated by hematite while those with < 30% k a o l i n i te are dominated by goethite. On an inter-regional scale, there is an apparent lack of relationship between l a t e r i t e formation and lithology. But on a smaller scale the l i t h o l o g i c a l control of the composition and form is more evident.

THE PHYSICAL, CHEMICAL, AND MINERAL0G1CAL PROPERTIES OF LATERITE SAMPLES FORMED IN VARIOUS ENVIRONMENTS

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