Trioctahedral minerals smectites

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... 

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. 

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. 

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... 

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 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.

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.

Silicates such as amorphous silica, trioctahedral smectite, and quartz, form in carbonate speleothems such as stalagmites, moonmilks, and crusts in the Guadalupe Mountains, New Mexico. In areas of relatively rapid carbonate mineral precipitation, amorphous silica was the common phase. In contrast, trioctahedral smectite and quartz formed where carbonate mineral precipitation was very slow and depositional conditions remained nearly constant for long periods of time. Other Mg-silicates such as kerolite formed in depositional environments between these two extremes. 

Polyak, V.J. and Giiven, N., 2000, Authigenesis of trioctahedral smectite in magnesium carbonate speleothems in Carlsbad Cavern and other caves of the Guadalupe Mountains, New Mexico, Clays Clay Miner, 48 317-321. 

Because they are the dominant mineral in shales, illites, and illite-smectites (see below) are the most abundant of all the clays. Illites are defined as micalike materials less than 2 yttm in size, which, like the micas, have a basal spacing of 10 A (Drever 1988). Most illites are dioctahedral and structurally similar to muscovite, although some are trioctahedral like biotite. Illites contain less and Al and more Si than muscovite. They also usually contain some Mg + and Fe, The irregularity of occurrence of interlayer K+ makes bonding between the layers weaker than in muscovite. Illitic clays... 

There is not much resistance to weathering in these minerals because of the relative lack of Si—O—Si bonding, especially in island silicates such as olivine. Layer silicate minerals rich in Mg (e.g., trioctahedral smectites, chlorite, serpentine) may form from the siliceous residue if leaching does not deplete in the weathering zone. 

Smectite group minerals, when present in the petroleum reservoirs, play an important role in the migration of hydrocarbons. At the shallow level of reservoir rocks smectite can exist, but at deeper level the increase of temperatiue transforms it to other minerals. Generally dioctahedral smectites are transformed to illite and trioctahedral smectites are transformed to chlorite, releasing the interlayer water molecules in both cases. That released water increases the pore fluid pressure that may lead to migration of the hydrocarbons. 

The two end members of this group with mainly tetrahedral substitutions are beidellite and saponite, which are di- and trioctahedral smectites, respectively. The corresponding end members with mainly octahedral substitutions are mont-morillonite and hectorite. Another common smectite, nontronite, is an iron-rich mineral. Chemical compositions of various smectite samples are provided in Table 2. Montmorillonite is the most common mineral of this group it is named for its location in Montmorillon, France. Figures 3d and 3e provide SEM views of the textural morphology of two montmorillonites. A common industrial mineral is bentonite, which is actually a montmorillonite of volcanic ash origin that contains a significant amount of impurities, such as cristobalite (a-quartz), that is intimately mixed with the clay. 

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