542 MINERALS/Glauconites Glauconites J M Huggett, Petroclays, Ashtead, UK and The Natural History Museum, London, UK ß 2005, Elsevier Ltd All Rights Reserved Green clay can be Fe smectite, glauconitic-smectite, smectitic-glauconite, berthierine, odinite (formerly phyllite v), a ferric chlorite (phyllite c), chamosite, ferric illite, or celadonite Although the environment of deposition can be a guide to identification, careful chemical and mineralogical analysis is required to unequivocally identify green clay minerals The green granule-forming clays are glauconitic, odinite, berthierine, or rarely chamosite, all forming where the rate of deposition is slow Glauconite is a green, ferric iron-rich micaceous mineral that forms in marine sediments Odinite and ferric chlorite are the ferric iron-rich precursors of the ferrous iron-rich clays berthierine and chamosite Together odinite and ferric chlorite comprise the verdine facies in recent sediments Odinite is only known from marine sediments, but berthierine and chamosite can be nonmarine An assemblage of mainly glauconitic granules is referred to as the glaucony facies, whereas an assemblage of mainly iron-rich 7-A˚ granules is called the verdine facies (although the latter term is used for recent assemblages rather than ancient ones) Composition Glauconite (sensu strictu) is an Fe-rich, K-rich dioctahedral mica with tetrahedral Al (or Fe3ỵ) usually >0.2 atom per formula unit and octahedral R3ỵ correspondingly >1.2 atoms Typically 5–12% of the total iron is ferrous (Table 1) The structural formula may be written as 3ỵ 2ỵ Kxỵy ịSi4 x ; Alx ị$4 Fe ; Al; Mg; Fe Þ$2 O10 ðOHÞ2 where x is 0.2–0.6 and y (the sum of the divalent octahedral cations) is 0.4–0.6 It is distinguished chemically from ferric illite in having more total iron, and from celadonite in having greater substitution of aluminium for silicon in the tetrahedral layer and a higher octahedral charge (Table 1) Glauconitic granules that have replaced faecal pellets are almost always inhomogeneous, with inclusions of common detrital minerals: clays, quartz, feldspars, carbonates, or apatite Glauconiticsmectite is a mixed layer clay that is less potassic than glauconite and which characterizes immature glauconitic granules Fe smectite is a ferrous iron-bearing dioctahedral smectite, half way between montmorillonite and nontronite (iron-rich smectite) Odinite is a poorly ordered, ferric iron-rich, 7-A˚ 1:1 green clay with $0.8 Fe3ỵ/Fe2ỵ ỵ Fe3 and low tetrahedra substitution of Al2O3 for SiO2 It is believed to be the precursor of the poorly – ordered, ferrous iron-rich, 7-A˚ green clay berthierine, which has 0.2 Fe3ỵ/ Fe2ỵ ỵ Fe3 and less Mg than odinite Phyllite C has Table Chemical composition of various glauconites 48.17 4.25 0.07 23.44 2.34 0.04 3.59 0.09 0.41 8.55 90.95 50.87 3.71 0.07 23.00 2.30 0.04 3.93 0.29 0.52 7.19 91.92 49.73 9.78 0.05 21.05 2.10 0.03 4.34 0.22 0.15 6.56 94.01 50.18 6.74 0.00 23.43 2.34 0.01 2.77 1.10 0.56 6.89 94.02 35.41 15.73 0.00 26.99 1.30 0.14 4.95 0.00 0.00 0.00 84.52 27.20 20.33 0.00 ? 37.96 0.00 2.97 0.00 0.00 0.00 88.46 Si Al Total tetrahedral 7.49 0.51 8.00 7.70 0.30 8.00 7.24 0.76 8.00 7.43 0.57 8.00 3.79 0.21 4.00 2.72 1.28 4.00 Al Ti Fe3ỵ Fe2ỵ a Mn Mg Total octahedral 0.27 0.01 2.51 0.30 0.01 0.83 3.93 0.36 0.01 2.39 0.29 0.01 0.89 3.95 0.92 0.01 2.09 0.26 0.00 0.94 4.21 0.60 0.00 2.39 0.28 0.00 0.61 3.89 1.76 0.00 2.40 0.12 0.00 0.79 5.07 1.12 0.00 3.01 0.00 0.00 0.44 4.57 Ca Na K Total interlayer 0.02 0.12 1.70 1.84 0.05 0.15 1.39 1.59 0.03 0.04 1.22 1.29 0.17 0.16 1.30 1.63 SiO2 Al2O3 TiO2 Fe2O3 FeOa MnO MgO CaO Na2O K2O Total Shallow water glauconite (Pliocene) from ODP leg 174 A, deep water glauconite (Oligocene) from ODP leg 174 A, smectitic glacuonite from the Weches Formation (Eocene, Texas), smectitic glauconite from the Karai Formation (Cretaceous, India) odinite from Weches Formation (Eocene, Texas), berthierine Interlayercations in berthierine are due to contamination by micaceous minerals Number of cations are on the basis of O20(OH)4 for glauconitic clays and O10(OH)8 for odinite and berthierine a FeO is assumed to be 10% of the total iron for glauconite, the odinite FeO is