Glauconite is a phyllosilicate (mica group) mineral of formula: (K,Na)(Fe3+,Al,Mg)2(Si,Al)4O10(OH)2. It crystallizes with monoclinic geometry. The name is derived from the Greek glaucos for the blue green color. Its color ranges from olive green, black green to bluish green. In the Mohs scale it has hardness of 2. The relative density range is 2.2 - 2.8. It is normally found in dark green rounded nodules of sand size dimension. It can be confused with chlorite or with some clays. Normally, glauconite is considered diagnostic of continental shelf marine depositional environments with slow rates of accumulation. It develops as a consequence of diagenetic alteration of biotite micas or volcanic glass. Glauconite forms under reducing conditions in sediments and is commonly found in nearshore sandstones.
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