Trioctahedral smectite

Clays and Other Sources. Sedimentary deposits, especially hthium-bearing clays found in the western United States, offer an additional source of lithium. These clays contain lithium-hearing trioctahedral smectites, of which hectorite [12173-47-6] NaQ23(Mg,Li)2Si402Q(F,0H)2, is one mineral. 

Vermicuhte is an expandable 2 1 mineral like smectite, but vermiculite has a negative charge imbalance of 0.6—0.9 per 02q(0H)2 compared to smectite which has ca 0.3—0.6 per 02q(0H)2. The charge imbalance of vermiculite is satisfied by incorporating cations in two water layers as part of its crystal stmcture (144). Vermiculite, which can be either trioctahedral or dioctahedral, often forms from alteration of mica and can be viewed as an intermediate between UHte and smectite. Also, vermiculite is an end member in a compositional sequence involving chlorite (37). Vermiculite may be viewed as a mica that has lost part of its K+, or a chlorite that has lost its interlayer, and must balance its charge with hydrated cations. 

The chemical composition of vermiculite can be quite variable (145). The megascopic varieties are generally trioctahedral, and the clay-si2e varieties contain both dioctahedral and trioctahedral varieties (144). Smectite minerals do not commonly occur as macroscopic single crystals. 

Fibrous saponite, with the analyzed chemical formula (Mgs g, AIq i, F o.i)(Si6.76> All o4 Fe 0.2) 02o(OH)4 IOH2O, also had Cao.i and Mgo4 as exchangeable ions (Midgely and Grass, 1956). Saponite is an example of a trioctahedral smectite. The variable chemical compositions of the smectites adds to the difficulties of accurate identification of these minerals. 

In the discussions that follow, the terms which will be used are montmorillonite = tetrasilicic expanding phase, dominantly octahedrally charged montmorillonites = the undefined expanding phase(s) dioctahedral or trioctahedral montmorillonite = smectite or saponite, respectively. 

The trioctahedral smectites are quite variable in composition, particularly in the octahedral sheet. The Mg-rich end member which contains little Al in either the octahedral or tetrahedral sheet has been called stevensite (Faust and Murata, 1953 ... 

The material from the Hector area of California is believed to have formed by the action of hot spring waters containing Li and F on clinoptiolite. The Mg was obtained from the alkaline lake waters (Ames and Goldich, 1958). The material from Morocco is associated with marls and is believed to be authigenic. These two types of trioctahedral smectite appear to be the only ones with a relatively pure Si tetrahedral sheet. No analyses were found which indicated tetrahedral Al values between 0.02 and 0.30. Analyses of saponite indicate there is complete isomorphous substitution between the range Si3.70 Al0.3o and Si3.0s Al0.92 (Table XXXIX). Caillere and Henin (1951) reported an analysis of a fibrous expanded clay (diabantite) which had a tetrahedral composition of Si3.i7 Alo.49 Fe3+0.34. There is some question as to whether this should be classified as a smectite regardless, it indicates the possibility of Fe3+ substitution in the tetrahedral sheets of the trioctahedral 2 1 clays. 

The upper limit for the number of R3+ cations in octahedral positions is essentially 0.50 or approximately 85% occupancy by R2+ cations. This compares with a minimum R2+ occupancy value of about 75% for trioctahedral micas (Radoslovich, 1963b) and 65% for dioctahedral smectites and illites. The composition of the octahedral sheet of the trioctahedral smectites falls within the compositional limits established for the trioctahedral micas (Foster,1960). All samples fall within the... 

The maximum amount of Al3+ tetrahedral substitution that 2 1 clays minerals formed at low temperatures can accommodate appears to be 0.80—0.90 per four tetrahedra. While this appears to place an upper limit on the amount of R3+ octahedral substitution, it is not clear why the limit should be such a low value. The dioctahedral smectites can accommodate more substitution (R2 + for R3+) in the octahedral sheet than can the dioctahedral micas. The reverse situation exists for trioctahedral equivalents. In the latter clays octahedral R3+ increases as tetrahedral Al increases. Thus, as one sheet increases its negative charge, the other tends to increase its positive charge. This is likely to introduce additional constraints on the structure. In the dioctahedral clays substitution in either sheet affords them a negative charge and substitution in one sheet is not predicted by substitution in the other sheet thus, one might expect more flexibility. 

A great many of the less common cations occur in the octahedral sheet of the trioctahedral smectites. Zn, Cr, Ni, Cu, Ti, Mn, and V have all been reported as occurring in significant amounts. The first five can occur as predominant ions. The zinc-bearing smectite, sauconite, is more common and occurs as a purer clay than any of these others. A number of these clays have been described by Ross (1946) and Faust (1951). Analyses of sauconite are reported by Ross (1946) some of these data are reproduced in Table XL along with two other analyses of impure samples. 

These clays have considerably more octahedial Al than any of the other trioctahedral smectites. Those with high octahedral Al (0.73—0.79) have a low octahedral population (2.70—2.80). These latter values are tl 3 lowest that have been reported for the clay minerals deposited from solution. A mil mum of approximately 60% of the... 

Chemical analyses of some trioctahedral smectites rich in Cr203 and CuO... 

Octahedral Mg, Al, and Fe3+ for the dioctahedral clays were totalled and the relative proportion calculated (atomic percent). Octahedral Mg, Al, Fe3+ and Fe2 + were totalled and the percent Fe2+ calculated. The distribution values for the 2 1 minerals are summarized in Fig.25. For comparison purposes, values for attapulgite and some trioctahedral smectites are also shown. 

Figure 1. Composition and classification of known end members of dioctahedral (A) and trioctahedral (B) smectites ...

The creation of Bronsted acid sites in a dioctahedral clay such as the beidellite, or a trioctahedral smectite, such as the saponite, is carried out using the same methodology previously explained for zeolites ... 

Chang H. K., Mackenzie F. T., and Schoonmaker J. (1986) Comparisons between the diagenesis of dioctahedral and trioctahedral smectite, Brazihan offshore basins. Clays Clay Min. 34, 407-423. 

Figure 6 Representation of chemical compositions of potassic, low-temperature micas in space. The poles represent feldspar, dioctahedral clays, and trioctahedral clays, respectively. M = Na, Ca, and especially K ions, R = Al, Fe R = Fe Mg. The compositional positions of the minerals Mu (muscovite) kaol (kaolinite), smectite, and mixed layer mica/smec-tites are indicated. Initial materials are kaolinite (kaol) and iron oxides. A second step is the production of an iron-aluminous smectite and then the formation of either illite via an iUite/smectite mixed layer mineral or glauconite via a glauconite mica/iron-smectite mixed layer phase.

A mixture of dioctahedral smectite and berthierine gives the mineral spacings for the 060 spacings observed by Bailey and Odin, which are between those of clearly aluminous dioctahedral and trioctahedral minerals. 

Berthierine, as shown by Brindley (1982) is essentially a trioctahedral mineral, following the line of trioctahedral chlorites in Figure 7. In our simulations of the XRD spectra of odinite, we use a ferrous serpentine and a ferric dioctahedral smectite component. Translated into constituent ions of a mineral structure, this mineral combination will give a bulk average composition between nontronite (ferric, dioctahedral smectite) and berthierine (trioctahedral chlorite). 

If we look back to the singular chemical features of odinite as having large amounts of ferric iron present and having an overall low occupation of the octahedral site for a trioctahedral mineral, a mixed layered mineral of ferric, dioctahedral smectite (nontronite), and berthierine (ferrous 7 A chlorite) would give the overall chemical characteristics of odinite. Thus, one can fit the XRD data by using a ferric... 

Figure 11 Representation of the evolution of clay pellets in shallow shelf sediment areas according to the oxido-reduction conditions locally present. Lower arrow shows berthierine formation through reduction of iron, shifting the pellet composition from the ferric (R = Fe ) pole to the ferrous pole (R = Fe ). This reaction passes through a chemical evolution by the formation of a berthierine/smectite mixed layer mineral (chi in the figure). The arrow towards glauconite indicates the change in composition with increase in potassium and some reduction of ferric iron. The diagram represents feldspar, dioctahedral clays, and trioctahedral clays, respectively. R + = Fe +, R = Al, Fe. The compositional positions of the minerals Mu (muscovite) kaol (kaolinite) and end-member celadonite (Ce) are indicated.

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