Iron Staining of Quartz Beach Sand in Southeastern Australia

Abstract

Although iron stains are a commonly described feature of marine sand grains, the micromorphology and mineralogy of these features has not been determined previously. Light microscopy, scanning electron microscopy and X-ray diffractometry were used in this study to examine the grain surface features responsible for the iron staining of quartzitic beach sand along the coastline of southeastern Australia. These iron stains consist of iron oxide enriched phyllosilicate clay coatings. Iron oxides coating directly onto the quartz grains were not observed indicating that the phyllosilicate clay coatings are a co-requisite for iron staining. The main iron oxide mineral present in these features was goethite with minor amounts of hematite. The phyllosilicate clays in these coatings are kaolinite and illite. These platy clays are embedded into the quartz sand and are usually oriented with their flat surfaces perpendicular to that of the grain surface.