Celadonite composition

Experimental work in the systems K-Mg-Si-Al-Fe- O concerning celadonites has also produced expandable minerals (Velde, 1972 Velde, unpublished). In both the muscovite-MgAl celadonite and MgFe-MgAl celadonite compositional series, fully expandable phases were produced below 300°C at 2Kb pressure. These expandable phases can coexist with a potassic feldspar (Figure 23). Their (060) reflection near 1.50 X indicates a dioctahedral structure which can apparently be intimately... 

Figure 23. Phase relations in the muscovite-MgAl celadonite compositional join, 2Kb pressure. (Velde, unpublished data.) M = dioctahedral mica ...

Celadonite [71606-04-7] is an iron-rich dioctahedral micaceous mineral that is similar to glauconite. Celadonite has a composition of (Na,K)Q... 

Figure 1. Representation of the ideal compositions of some major phyllosilicate phases in the MR - 2R - 3R coordinates. M = muscovite, paragonite P - phlogopite Py = pyrophyllite Kaol = kaolinite S serpentine T = talc Chlor = chlorite, 14 8 or aluminous 7 8 polymorphs Ce = celadonite F = feldspar.

Figure 5. Typical X-ray diffraction traces of the (001) reflection for mica and mica-illite minerals. Assymmetry is shown towards large values. A - natural 2M muscovite B = natural illite (IMd) C - synthetic illite (lMd), 75% mica, 25% prophyllite composition D = synthetic 1M muscovite E - natural 1M glauconite F = synthetic 1M celadonite mica.

Natural mica compositions of the dioctahedral, potassic types have been discussed by Velde (1965b) in connection with the solid solution between muscovite and the different celadonite mica molecules. It was shown that both natural and synthetic micas formed two distinct compositional and genetic groups. The important point made in the discussion is the definition of the term mica. The most restrictive criteria as was mentioned before is the necessity for the mineral in question to have a net charge (the sum of octahedral and tetrahedral electrostatic... 

Figure 6. Mica phases produced from compositions in the series muscovite-MgAl celadonite (Velde, 1965b). Si = silica content of the mica produced where Si q = muscovite, Si q = celadonite.

Figure 7. Phases present along the compositional join muscovite (Mu)— MgFe +. celadonite (Ce) at 2Kb pressure. MU = muscovite-phengite Mica = dioctahedral mica of unidentified composition CE = celadonite mica ...

Figure 8. Compositions of natural potassic micas as a function of their AlVI—Fe + contents (octahedrally coordinated ions). Crosses represent phengite micas and dots celadonite-glauconite micas (K + Na + Ca/2 =...

The mineral types familiar in sediments and sedimentary rocks are present micas, mica-like phases, fully expandable phases and mixed layered series. In a sense, celadonite mica is isolated from dioctahedral mica by a multiphase zone where montmorillonite is stable with a feldspar and mica. It is evident that the only way to. produce celadonite mica under high potassium concentrations is by having a proper bulk composition toward that of celadonite. The possibility of producing celadonite in a potassium deficient system, i.e., where montmorillonite coexists with a non-alkali bearing phase, has not yet been studied experimentally. 

The bulk compositions of natural illite, celadonite and glauconite ... 

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.

However, it is evident that the celadonite-glauconites form a continuum between the tetrasilicic mica composition, illite and dioctahedral... 

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.

Alterations of basic or intermediate composition eruptive rocks giving celadonite and related minerals (Peyrone, et al , 1965 Pirani,... 

Figure 26. Compositional fields of natural mixed layered minerals compared to theoretical end-members (shaded area). Mu = muscovite B = beidellite Mo = montmorillonite Ce = celadonite.

If we now consider the bulk compositions of the mixed-layered minerals which contain both expandable and non-expandable layers, two series are apparent, one between theoretical beidellite and illite and one between theoretical montmorillonite and illite (Figure 25). The intersection of the lines joining muscovite-montmorillonite and beidellite-celadonite (i.e., expandable mineral to mica), is a point which delimits, roughly, the apparent compositional fields of the two montmorillonite-illite compositional trends for the natural mixed layered minerals (Figure 26). That is, the natural minerals appear to show a compositional distribution due to solid solutions between each one of the two montmorillonite types and the two mica types—muscovite and celadonite. There is no apparent solid solution between the two highly expandable (80% montmorillonite) beidellitic and montmorillonitic end members. The point of intersection of the theoretical substitutional series beidellite = celadonite and muscovite-montmorillonite is located at about 30-40% expandable layers— 70-60% illite. This interlayering is similar to the "mineral" allevardite as defined previously. It appears that as the expandability of the mixed... 

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... 

C eladonitc is an iron-rich dioctahedral micaceous mineral that is similar lo glauconite. Celadonite has a composition of (Na, Kla.s.tlFc. Alj M6i)(,vFc o.2o)r.ns(Si.i siAln,io)Oui(OH)i (39) and. like glauconile. has well crystalline, poorly crystalline, and inlerslratilied varieties. 

Dioctahedral micas (alkali interlayer ions having total charge near +1 per formula weight) which have either lMd or 1M polymorphs are either metastable muscovite forms or are micas with a composition differing from muscovite, e.g., glauconite, celadonite, and illite. ... 

Celadonites commonly have 0.00-0.30 tetrahedral A1 (Fig. 10) whereas most glauconites have between 0.25 and 0.60 (Fig.5). The smallest value reported for glauconite is 0.11 but 23 of the 82 glauconite analyses collected have less than 0.30 tetrahedral Al. Thus, there is considerable overlap and the composition of this sheet can not be considered exclusively diagnostic. It is more likely that there is a continuous series with two well developed modes. 

In general, when either Al or Fe3+ is the dominant (greater than 1.0) cation in the octahedral sheet of a 2 1 dioctahedral clay, the maximum Mg content the sheet can accommodate is 0.50-0.60 (0.5 if Fe3+ is dominant and 0.6 if Al is dominant). When the Mg content is larger than 0.6, as for most celadonites, seldom is any other cation present in amounts greater than 1.0. This suggests structural control of composition. 

There is sufficient overlap of the composition of celadonite and glauconite to indicate that there is a continuous series and that a genetic classification, while useful, is not definitive. 

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