Alkali-rich

Alkali-rich portions of Na20-Nb20s or Na20-Ta205 systems oxides in LiF melt... 

As we have demonstrated, IEX reactions occur independent of the saturation state of the aqueous solution, raise the local solution pH, and so cause additional glass dissolution via reaction (6). The residual rate for alkali-rich glass compositions, therefore, is simply the net rate of glass dissolution controlled by the rate at which the ion-exchange reaction proceeds. 

Fe2+ R3 - Fe3+, Al3+, Ti4+ M+ = Na+, K+ and 2 x Ca2+. An M+R3 pole represents the bulk composition of feldspars, commonly found associated with clay minerals. They are the most alkali-rich minerals present (excluding zeolites). Calcium is considered to fulfill a chemical role similar to the alkali ions in most clay minerals. It is notably not present in micas stable at low temperatures (Velde, 1971, Hemley, ejt al., ... 

Reported assemblages in sedimentary rocks containing analcite and potassic feldspar plus an alkali zeolite (Hay, 1966 Sheppard and Gude, 1968, 1969 Moiola, 1970) lead to the construction of an intermediate paragenesis which denotes a more restricted range of alkali zeolite solid solution, notably the instability of the alkali-rich phase phillipsite. 

Since neither mineral is conspicuously alkali-rich, the M R -2R -3R plot is not appropriate to represent their bulk compositions. Both sepiolite and palygorskite contain small but variable amounts of Ca, Mg,... 

Since alkalis enter into the structure of these two minerals in only small quantities, these variables can be ignored in a first approximation. The associations of alkali-rich and alkali-poor systems will be discussed later. 

Ceramic glazes have three basic components silica, a flux used to lower the melting point of the silica, and a colorant. In Mesopotamia, sources of silica include crushed and sifted mineral quartz or quartz-rich sands. Two different types of fluxes are used. One is based on the use of the ashes from alkali-rich plants and the other on lead oxide. Colorants were derived from metallic oxides, the sources of which include native ores and debris from metal-crafting (2, <5, 7). 

Various surface analysis techniques show that silicate glasses rapidly develop surface compositional profiles when exposed to water. When water is present as a vapor an alkali-rich layer (presumably a hydrated alkali carbonate) forms over the SiOj-rich layer. Water as a liquid dissolves the alkali and leaves the silica-rich film. As long as this SiC -rich film is stable the rate of corrosion due to diffusion is reduced with exposure time. Addition of multi-valent species to the glass or reactant results in formation of a complex protective surface layer in the glass which may be stable over a wide range of environmental conditions. 

The alkali cations in pfa normally occur almost entirely in the glass, and when the latter reacts may be presumed to enter the alkali-rich silicate that appears to be the initial product. When this phase is decomposed by reaction with Ca, they will be distributed, like alkali cations from any other source, between the solution and the solid hydration products, on which they are probably adsorbed (Section 7.3.2). The C-S-H tends to take them up more strongly as its Ca/Si ratio decreases (BI58,G63) consequently, the alkali cations released from the pfa are less effective in raising the OH concentration of the pore solution than are those released from the cement. The method outlined in Section 7.5.2 for calculating the OH concentration in the pore solution of Portland cement mix was extended to cover Portland-pfa cement mixes taking this into account (T37). 

Glass altered to alkali-rich zeolites (except analcine)... 

Haggerty S. E. (1989) Upper mantle opaque mineral stratigraphy and the genesis of metasomites and alkali-rich melts. In Kimberlites and Related Rocks. Geological Society of Australia Special Publication No. 14 (ed. J. Ross). Blackwell, Perth, vol. 2, pp. 687-699. 

Yang H., Konzett J., and Prewitt C. T. (2001) Crystal structure of phase X, a high pressure alkali-rich hydrous silicate and its anhydrous equivalent. Am. Mineral 86, 1483-1488. 

Most samples from full-scale installations show bed material grains on which (alkali-rich) surface coatings have lead to agglomeration. These samples indicate that coating thickness and chemical composition are important parameters. Therefore, further static heating experiments were conducted with coated (mullite) bed material. 

Stuckless, J.S. and Nkomo, I T., 1978. Uranium-lead isotope systematics in uraniferous alkali-rich granites from the Granite Mountains, Wyoming implications for uranium source rocks. Econ. Geol., 73 427-441. 

Nepheline syenite an alkali-rich, silica-depleted igneous rock emplaced below the earth s surface. 

In many of the samples in the alkali-rich zone the alkali literally fills all pores in the structure. Thus, one possible mechanism of alkali disruption may involve alternative freezing and thawing of this alkali. During cooling, alkali freezes and then cracks, which forms voids. If more molten alkali penetrates into these voids as the temperature of the hot face is increased, then all voids are filled before the frozen alkali can melt. When the original alkali does melt there is no place for the alkali to migrate or expand thus structural disruption may result. 

Solid-Liquid-Vapor Interactions in Alkali-Rich Coal Slags... 

The first glasses were made by mixing silica-rich sand with alkali-rich plant ashes or naturally occurring alkali-rich minerals, along with some lime, either as natural material in the sand or as deliberately added limestone. Thus a lot of early glass has compositions a lot like that of obsidian, i.e., about 70% silica, 15% Na O-i-K O, and 10% CaO-i-MgO. Most glass produced today still has this basic soda-lime composition. 

We suspect that the lack of alkali nitrides on the one hand and of transitional metal nitrides on the other hand led to the neglect, until recently, of a very rich ternary nitride chemistry. We have recorded here some remarkable nitrides (mostly reported rather recently) containing transition metal and alkali metals. We suspect that some of them were made serendipitously, as crucibles of elements like iron are often used to contain alkali-rich materials (such as Li, N). We observe that many ternary etc. oxides of elements such as Pt were similarly discovered as products of reactions in precious metal crucibles. 

This system is represented by a closed basin, made of impermeable rocks and filled in the past by a saline alkaline lake. Water in this case could not permeate downwards but only evaporate, so the deposit develops horizontally, instead of vertically as in the previous occurrence. Here pH and salinity in the fluids tend to increase, giving rise to brines, c.g., basic, alkali-rich solutions. Concentric zones of authigenic minerals are so formed, from an outer and upper ring of little altered glass and clay minerals, to zeolites, analcime and a finally alkali-feldspars. A good example for this type of occurrence is Lake Tecopa, California, where the zeolitic ring is constituted by phillipsitc, clinoptilolite and erionite, followed by the central feldspar zone [36]. 

Hazen RM, Finger LW (1978) The crystal stractures and compressibilities of layer minerals at high pressure. 11. Phlogopite and chlorite. Am Mineral 63 293-296 Hazen RM, Finger LW, Velde D (1981) Crystal stracture of a sihca- and alkali-rich trioctahedral mica. Am Mineral 66 586-591... 

Explosive volcanism in western North America 95 million years ago (Late Cretaceous age 42) spread volcanic ash downwind to the east of the volcanoes. Upon deposition, the volcanic ash was chemically altered (e.g., devitrification of volcanic glass) to form bentonite, in which montmorillonite is the dominant mineral. In addition, the Late Cretaceous bentonites contain low abundances of magmatic minerals (e.g., quartz, alkali-rich feldspar, zircon, biotite) that were quenched during the volcanic eruption 43, 44) and entrained in the volcanic ash. The explosive volcanic events are known to have produced ash having a granitic composition 40). 

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