The term "glauconie" refers to any of a number of green clay minerals ranging from the mineral glauconite with an ordered or disordered dioctahedral micaceous lattice to a variable mixture of illite, montmorillonite, or chlorite. In the literature the depths of glauconie occurrence have been described as being restricted to between 30 and 2000 m. Various modes of formation of glauconie have been outlined including neoformation inside foraminifera shells and transformation of biotite. The study of sediments from DSDP Leg 29 revealed the occurrence of glauconie in significant amounts at sites 275, 277, 280, 280 (Hole 280A), and 281, showing a depth range from 1200 to 4200 m. At these sites the occurrence of glauconie includes detrital grains, internal molds and fillings in foraminifera, and transformed biotite.