Phlogopite ratios

Figure 5.51 fo2 stability field of biotite. (A) Pseudobinary phlogopite-annite mixture. Numbers at experimental points indicate observed Fe/(Fe + Mg) atom ratio. (B) Annite. HM = hematite-magnetite buffer NNO = Ni-NiO buffer MW = magnetite-wuestite buffer QFM = quartz-fayalite-magnetite buffer. From Wones and Eugster (1965). Reprinted with permission of The Mineralogical Society of America. 

The analysis of 29Si MAS NMR spectra of layer silicates with a wide range of tetrahedral compositions (Si/Al ratio 2.7-1.7) indicates (483, 486) that the distribution of Si and Al in these materials is indeed determined by (i) the local balance of charges, and (ii) the Loewenstein rule. In muscovite, phlogopite, and vermiculite, aluminum is randomly distributed in... 

Mica. Mica, usually phlogopite, is the dominant host for rubidium and barium in the mantle but has highly variable Rb/Sr (0.13-60) and Ba/Sr ratios (Ionov et al, 1997). As with amphibole, the... 

There have been relatively few systematic descriptions of noble gas concentrations in rocks and minerals. In general, the He content is dependent upon the abundances of Th and U, the crystal density of host minerals and the permeability of the rock. Mantle-derived rocks and minerals seem to be relatively enriched in He, with high He/ He ratios. Thus, minerals and nodules in kimberlites can have He contents up to 2755 cm /g x 10 (phlogopite) and 350 cm /g x 10 (diamond) in contrast, many igneous rocks may contain <0.1 cm /g X 10 (Hoppe and Alexander, 1978). Very high concentrations of He can occur... 

In some naturally occurring true micas. Si nearly fills all the tetrahedral sites (e.g., polylithionite, tainiolite, norrishite, and celadonite), whereas in the most common mica species (i.e., muscovite and phlogopite) Al substitutes for Si in a ratio near 1 3. In some true micas and brittle micas, the Al for Si substitution corresponds to a ratio of Al Si = 1 1 (e.g., ephesite, preiswerkite, siderophyllite, margarite, and kinoshitalite), whereas the... 

Another study by Sanz and Serratosa that same year [12] reached similar conclusions for some other 2 1 clays, but in addition they found that second nearest neighbors to the Al (namely the metals in adjacent octahedra) seemed to have a measurable effect on the Al chemical shifts. The clays studied were low in Fe (< 1%) and were purposefully chosen to represent three extremes pyrophillite should have only Al , muscovite should contain both Al and Al, while the phlogopite should contain only Al,. Despite the obvious difficulties of quantitation, it was found that for the trioctahedral clays (with few Al in the octahedral positions, mainly filled by Mg), the line for the octahedral Al shifted upfield to around 5-6 ppm, whereas for the dioctahedral clays (with only Al in the octahedra), a shift around 1-2 ppm was common. Differences were also observed for the Al, depending on the composition of the octahedral layer. Thus it was clear that Al NMR could be used for more than simply trying to determine the AI,/A1 ratio. There was no discussion in this brief paper concerning whether the observed shifts were indeed chemical shifts or second-order quadrupolar shifts. 

Mica is a generic name to describe a group of complex hydrous potassium aluminate silicate materials, differing in chemical composition, but sharing a unique laminar crystalline structure. In nature, mica develops in a book-like form. The individual platelets can be delaminated into very thin high aspect ratio particles that are tough and flexible. Of the commercially important forms, muscovite and phlogopite are used as reinforcements for plastics. 

Higher amounts of iron in phlogopite mica bond the individual layers of mica together with relatively high forces. Because of this, books of phlogopite mica are more difficult to delaminate than books of muscovite mica, and resulting aspect ratios are somewhat lower. 

Naturally occurring micas have a variety of chemical compositions and morphologies. Three major types are commercially available for use in polymers wollastonite, muscovite, and phlogopite. Mica particles are sometimes fiber shaped, but more commonly platelet or flake shaped. Their aspect ratio (width-to-thickness ratio) plays an important part in the reinforcement properties. 

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