Celadonite

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

Distinctions between glauconite and celadonite may be vague in the area of approximately 0.2% tetrahedral Al. Celadonite is found as an alteration mineral in mafic volcanic rocks (127). 

Figure 3. Plot of 10 1nP56/54 values versus 10 /7 (K) for (A) Fe minerals calculated from Polyakov and Mineev (2000), and for (B) aqueous Fe species calculated from Schauble et al. (2001). Temperature scale in °C shown at top. Mineral abbreviations are Py pyrite, Mt magnetite, Celad celadonite, Hem hematite, Goe goethite, Lepid lepidocrocite, 01 olivine, Sid siderite, Ank-2 ankerite (Cai iMg ,jFe ,3Mn ,i(C03)2), Ank-1 ankerite (CaiMgo,5Feo,5(C03)2).

During this zone refining, the primary (igneous) rocks are transformed into secondary minerals. These include (1) clay minerals, such as phillipsite, chlorite, montmo-rillonite (smectite), saponite, celadonite, and zeolite (2) iron oxyhydroxides (3) pyrite (4) various carbonates and (5) quartz. These minerals form rapidly, within 0.015 and 0.12 million years after creation of the oceanic crust at the MOR. During these alteration... 

The palagonite is thermodynamically unstable and, hence, reacts with seawater to form various clay minerals, including smectites (montmorillonite, nontronite, and saponite), micas (celadonite), and zeolites (phillipsite). This chemical weathering involves uptake of Si, Al, Mg, Ca, Na, and K and the release of water, reversing to some extent, the elemental effect of palagonitization. These mineral alterations tend to proceed progressively from the outer margin of the pillow basalts to their interior. 

Because of the relative scarcity of lithogenous particles and fast seafloor spreading rates, metalliferous sediments are common around the East Pacific Rise and very high densities of manganese nodules are present on the abyssal plains, especially in the Southern Hemisphere. In these locations, the weathering products of volcanic detritus, such as montmorillonite, phillipsite, nontronite, and celadonite, are also found in great abimdance. 

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.

The main method used to distinguish the relative quantities of neoformed illite is by the polymorph or structure of the material. Using the criteria that 2M and 3T polymorphs of dioctahedral potassic mica are high temperature forms (Velde, 1965a), the determination of the relative quantities of lMd, and 1M vs. 2M, 3T polymorphs permits a semi-quantitative estimation of the proportion of neo-formed or low temperature illite present in a specimen. A method commonly used is a determination of relative intensities of X-ray diffraction peaks of non-oriented mica (Velde and Hower, 1963 Maxwell and Hower, 1967). Usually only 2M and lMd polymorphs are present in illite specimens which simplifies the problem. The 1M polymorph is typical of ferric illites and celadonite-glauconites, the more tetrasilicic types. 

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... 

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