glauconiteA clay mineral of the illite type, a hydrated mica containing iron, magnesium and aluminum. Glauconite is formed by alteration of biotite in a shallow reducing, marine environment, it commonly occurs as small green pellets in sedimentary deposits. Greensand is a mixture of glauconite with quartz sand. Related category GEOLOGY AND PLANETARY SCIENCEAlso on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History |