Montmorillonite glauconite

Lee SY, Jackson ML, Brown JL (1975a) Micaceous occlusions in kaolinite observed by ultrami-cotomy and high resolution electron microscopy. Clays Clay Miner 23 125-129 Lee SY, Jackson ML, Brown JL (1975b) Micaceous vermicuUte, glauconite and mixed-layered kaolinite-montmorillonite by ultramicotomy and high resolution electron microscopy Proc Soil Sci Soc Amer 39 793-800... 

Figure 13. Celadonite-glauconites as a function of their composition in the MR - 2r3 - 3r2 coordinates. It is important to remember that glauconites contain large quantities of Fe +. Crosses are celadonites and circles glauconites. Mo = montmorillonite Ce = celadonite mica Mi = muscovite.

Figure 14. Fe and A1 in octahedrally coordinated sites of illite, celadonite and glauconites. M-B = muscovite beidellite theoretical compositions Mo = montmorillonite (octahedral charge) Ce = celadonite open circles = illite triangles = glauconites dots = celadonites.

The approach used is to compare the composition of mixed layered mineral series—the illite-montmorillonite and the glauconite-montmorillonites. 

A striking example of iron-enrichment of a detrital silicate material is presented by Giresse and Odin (1973). Recent, kaolinite-rich sediments containing about 8% Fe total on the West African Continental Shelf, are transformed into pellets rich in montmorillonite which contain 16-21% total iron. This material is then progressively enriched in potassium to form glauconite. 

Figure 15. Alkali (weight percent K2O + Na20) versus percent expandable layers in the illite—and glauconite-montmorillonite mineral series.

Figure 17. Proposed phase relations where K is a mobile component and Al, Fe are immobile components at about 20°C and several atmosphere water pressure for aluminous and ferric-ferrous mica-smectite minerals. Symbols are as follows I illite G = non-expanding glauconite Ox = iron oxide Kaol = kaolinlte Mo montmorillonite smectite N nontronitic smectite MLAL aluminous illite-smectite interlayered minerals Mlpe = iron-rich glauconite mica-smectite interlayered mineral. Dashed lines 1, 2, and 3 indicate the path three different starting materials might take during the process of glauconitization. The process involves increase of potassium content and the attainment of an iron-rich octahedral layer in a mica structure.

It is obvious then that A1 is not synonymous with Fe in sedimentary mica-like minerals. The increasing influence of trivalent iron in a sedimentary system will obviously provoke the crystallization of a specific mineral series which is not contiguous with illite and which would not be present otherwise. The development of glauconite in sediments should be due to specific local conditions which permit the chemical evolution of an initial montmorillonite material to celadonite mica-like phase. In fact previous observations have consistently led to this conclusion as to the origin of glauconite in sediments and sedimentary rocks. 

Two phase assemblages of any of these minerals are known. It should be noted that aluminous phases, such as kaolinite, have never been reported with corrensite neither are sedimentary phyllosilicates such as 7 8 chlorite or glauconite. Non-phyllosilicates in association with corrensite frequently include diagenetic quartz, albite and dolomite. Pelitic rocks, specially associated with those containing corrensite, contain allevardite and fully expanding montmorillonite (dioctahedral). 

Most commonly, zeolites are found in series of sedimentary rocks which contain pyroclastic material and are formed during the devitrification of this material. If the rocks are silica-rich, the zeolite species formed seems dependent upon the bulk composition and burial depth or temperature of formation (Hay, 1966). They are most frequently accompanied by silica in an amorphous or cryptocrystalline form (opal, chalcedony). Analcite and all other compositional intermediates up to the silica-rich clinoptilolite are found in this association. The most comifton clay mineral in such tuffs is montmorillonite. Zeolites are sometimes found with glauconite (Brown, et al . 1969) or celadonite (Hay, 1966 Iijima, 1970 Read and Eisenbacher, 1974) in pelitic layers or acidic eruptive rocks... 

Figure 2. Projection on planes Na—K—Mg and Ca—K—Mg of the composition of possible equilibrium phases and of marine sediment minus carbonate. CH = chlorite, IL — illite (hydromica), = montmorillonite, PH = phillipsite, SED = sediments [according to Goldschmidt (7)], CA = average calcareous, SI = average siliceous, AR = average argillaceous sediments (from Ref. 22), OW = ocean water, GL = glauconite,...

Mixed-layer illite-montmorillonite is by far the most abundant (in the vicinity 90%) mixed-layer clay. The two layers occur in all possible proportions from 9 1 to 1 9. Many of those with a 9 1 or even 8 2 ratio are called illites or glauconites (according to Hower, 1961, all glauconites have some interlayered montmorillonite) and those which have ratios of 1 9 and 2 8 are usually called montmorillonite. This practice is not desirable and js definitely misleading. Other random mixed-layer clays are chlorite-montmorillonite, biotite-vermiculite, chlorite-vermiculite, illite-chlorite-montmorillonite, talc-saponite, and serpentine-chlorite. Most commonly one of the layers is the expanded type and the other is non-expanded. 

In nature the Fe-rich illites (glauconite and celadonite) appear to progress from the lMd to the 1M polytype. The Al-rich illites are predominantly the lMd and 2M varieties. If the 1M polytype is an intermediate phase, it is surprising that it is not more abundant in sediments. Recent studies of unmetamorphosed Precambrian sediments (Reynolds,1963 Maxwell and Hower,1967) have shown that the lMd polytype is relatively abundant in ancient sediments, particularly in the extremely fine fraction. The senior author has noted the relative abundance of the lMd polytype in the fine fraction of most Paleozoic rocks but has considered most of it to be mixedlayered illite-montmorillonite rather than illite. Weaver (1963a), Reynolds (1965), and Maxwell and Hower (1967) have shown that during low-grade metamorphism water is squeezed from the expanded layers and the lMd polytype is transformed into the stable 2M polytype. 

The converse is true of the Mg ion. It is more abundant in the octahedral sheets of the low-temperature 2 1 dioctahedral minerals, attaining an average value of 3.55% in the montmorillonites and even higher values in glauconite and celadonite. Mg in the octahedral position increases the size of the octahedral sheet and decreases structural strain. 

Divalent iron is considerably more abundant in glauconite than in illite and montmorillonite although the Mg content of glauconite is similar to that of mont-morillonite. Octahedral Fe3+ is five times more abundant in glauconite than in illite and montmorillonite, and octahedral A1 is less than one-third as abundant. The total number of trivalent ions in the octahedral position averages 1.45 as compared to 1.76 for montmorillonite and 1.68 for illite. The distribution of total trivalent ions in the octahedral sheet of glauconites is approximately normal (Fig.5). Reported values ranged from 1.15 to 1.89 however, as with the A1 2 1 clays, there is a deficiency of values less than 1.30. 

Dyadchenko and Khatuntzeva (1955) and Keller (1958) give analyses of nonmarine glauconites altered from montmorillonite and feldspar, respectively. 

In Fig.30, the dividing line between predominantly octahedral charge and predominantly tetrahedral charge approximately coincides with the boundaries separating the A1 and Fe clays (illite-glauconite and montmorillonite-nontronite). Actually a simplified division (Fig.31) based on the 0.7 charge boundary and the boundary between predominantly octahedral and predominantly tetrahedral charge coincides well with the divisions based on the plotted data. 

Figure 9. Optical spectra of glauconite and iron-bearing montmorillonite showing the band near 14,000 cm"1 due to Fe2+- Fe intervalence charge transfer.

McCammon CA (1994) A Mdssbauer milliprobe Practical considerations. Hyper Interact 92 1235-1239 McConchie DM, Ward JB, McCann VH, Lewis DW (1979) A Mdssbauer investigation of glauconite and its geological significance. Clays Clay Minerals 27 339-348 Melankholin NM (1948) The coloration of micas. Doklady Akad Nauk SSSR 4 223-229 Michael PJ, McWhinnie WR (1980) Mdssbauer and ESR studies of the thermochemistiy of illite and montmorillonite. Polyhedron 8 2709-2718... 

Muscovite Igneous and metamorphic rocks Crystallization mostly under higher pressure-temperature conditions To illite, montmorillonite and glauconite Residual... 

Smectite group (montmorillonite, beidellite, nontronite, etc.) Silicatic rocks of either origin a) Incomplete leaching of silicates (feldspars, micas) due to restricted water drculation b) After deposition either by removal of potassium from micas or neoformation from solutions To kaolinite by subsequent leaching, to illite or glauconite by addition of potassium and iron, to chlorite Either residual or neoformation... 

J.H. Johnston, C.M. Cardile, Iron substitution in montmorillonite, illite and glauconite by pe Mossbauer spectroscopy. Clays Clay Miner. 35, 170-176 (1987)... 

Chlorite minerals have been identified in green earfti (. v.) pigments rich in glauconite, together with members of the clay minerals group, in particular iUite and montmorillonite ((qq.v.) Grissom, 1986). 

Chlorite group Clay minerals group Magnesium group Sheet silicates group Biotite Celadonite Enstatite Glauconite Green earth Illite Montmorillonite... 

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