A field study was conducted in western Puerto Rico to determine whether a correlation exists between the environment of occurrence of tropical soils and their electrical behavior. Soil samples were collected across the western end of the Cordillera Central from the vicinity of Isabella on the north coast to the vicinity of Parguera on the south coast of the island and along roads in an east-west direction joining the main traverse. Laboratory measurement of the electrical conductivity at 3 kHz was made in addition to the determination of the principal chemical and physical properties relevant to electrical behavior. X-ray diffraction analyses were made for several representative soils of the upland and lowland areas and for six pure clay specimens which were representative of the kaolin and montmorillonite groups.
The results of the field study indicate a clear correlation of the electrical conductivity of the soil to the clay mineral content and to the environment of clay mineral occurrence. High electrical conductivity of the soil was associated with the occurrence of montmorillonite-type clays, while low conductivity occurred in association with the kaolin-type clay minerals.