Trioctahedral minerals hectorite

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. 

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. 

Two types of crystallographic filling of the octahedral metal site characterize the structural filling. In the case of talc, hectorite, some vermicu-lite, and some micas, all three crystallographic sites are occupied by divalent ions such as magnesium. These are normally designated by the term trioctahedral. The other minerals only have cations at two out of the three sites and are referred to as dioctahedral. The predominate cation in these cases is Al " " or, in some cases, Fe ". ... 

The other key difference is the level and type of isomorphous substitution in each of these minerals. Among the trioctahedral clays, talc has no isomorphous substitution, hectorite has moderate substitution of Li for Mg and vermiculite and mica have high levels of substitution. 

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