Mineral Assemblages of the Sediments of the Ala Wai Canal and Its Drainage Basins, O'ahu, Hawai'i

Abstract

To understand the origin of the mineralogy of the sediments in the Ala Wai Canal, 20 soil and stream sediment samples were collected from Manoa, Palolo, and Makiki Valleys. X-ray diffraction analysis was used to determine mineralogical composition. Four mineral assemblages are recognized: plagioclase from mechanical weathering present in Makiki Valley and pyroxene, olivine, plagioclase, and ilmenite in Manoa and Palolo Valleys; (2) maghemite, hematite, and kaolinite present in all three valleys from chemical weathering and gibbsite and goethite in Manoa Valley and goethite in Palolo Valley; (3) quartz in all three valleys from aeolian deposition; and (4) pyrite, calcite, and aragonite in the Ala Wai Canal, and kaolinite and gibbsite derived from the watershed studied.