Feldspathoid

Cancrinites are one of the rarest members of the feldspathoid group, classified as such due to its low silicon content. However, cancrinite is also classified as a zeolite, due to its open pore structure, which confers molecular sieve properties [1], Likewise, variable sodium carbonate and NaOH concentrations in the hydrothermal synthesis of cancrinite could direct the synthesis of the intermediate phase or the disordered cancrinite formation [2], The intermediate phase is described as a phase between cancrinite and sodalite [3], The disordered cancrinite is an intermediate phase which is much closer to the cancrinite structure than sodalite structure [2],... 

In contact-metamorphic zones, in association with magnetite and Fe-rich silicates (feldspathoid-bearing igneous rocks)... 

Bellatreccia, F., Della Ventura, G., Williams, C. T., Lumpkin, G. R., Smith, K. L. Colella, M. 2002. Non-metamict zirconolite polytypes from the feldspathoid-bearing alkali-syeni-tic ejecta of the Vico volcanic Complex (Ladum, Italy). European Journal of Mineralogy, 14, 809-820. 

Yund, R.A. (1984) in Feldspars and Feldspathoids Structure, Properties and Occurrences (Ed. W.L. Brown), D. Reidel Publ. Comp., Dordrecht... 

Silicates. This mineral classification encompasses the largest group of mineral species and includes most of the important rock-forming minerals, such as the feldspars, feldspathoids, pyroxenes, amphiboles. 

Brown. W.L., Editor Feldspars and Feldspathoids, Re idol. Boston, 1984. Campbell. A N. el ol. "Recognition of u Hidden Mineral Deposit by an Artificial Intelligence Program,". Viemr. 217. 927-029 tl982). 

These were remarkable accomplishments considering the size of the unit cells and the complexity of the structures. I remember posing the problem to Dr. Linus Pauling when he visited our laboraory in the mid fifties. Some 25 years earlier he had published on the structure of the zeolite natrolite and several feldspathoids [22]. He assured me that it was a waste of time to even try to determine the detailed structure of zeolites from powder x-ray data. 

Transmission electron microscope investigations of the microstructures of microclines. In Feldspars and Feldspathoids, Structures, Properties and Occurrences, edited by W. L. Brown, pp. 373-409. Dordrecht D. Reidel. 

The principal secondary minerals in CM CAIs are diverse phyllosilicates (cronstedite, serpentine, and the Fe-Ni-S-O phase tochilinite see review by Tomeoka et al, 1989) and calcite. Feldspathoids have only rarely been reported (MacPherson et al, 1983 El Goresy et al, 1984). 

K-Rb-Cs leucite. The much-studied feldspathoid leucite (KAlSi206) provides an example of the close correspondence between polymorphic and morphotropic displacive transitions. Leucite readily accommodates substitutions of its alkali cation, and... 

In systems G and H, sodium sulfate was used as a sodium source mixed with kaolinite and calcium acetate. Sodium sulfate melts at approximately 884 C. Therefore, at 750 C no interaction between kaolinite and sodium sulfate was seen (systems G and H). In system G nepheline was formed at 1000 C, with none of the sulfur released from the sodium sulfate involved in the formation of any new high temperature minerals. However, in system H additional feldspathoids (i.e., gehlenite and hauyne) other than nepheline were formed. In this case, sulfur was involved in forming new high temperature minerals. 

In systems A through I the major aluminosilicate minerals produced were silica-deficient. However, in systems J where silica was provided in excess in the form of quartz the system still produced only feldspathoids containing only two-thirds as much silica as their silica-rich counterparts (i.e. alkali feldspars). In addition, the quartz peaks in system J were not substantially reduced at higher temperatures. These two facts suggest that SIO2 in the form of quartz is inactive up to and at 1000 C. This idea is supported by the fact that quartz peaks are also quite evident in diffractometer patterns of ash samples generated between 750% and 1000 C. It appears that temperatures in excess of 1000 C are required for quartz to contribute to the formation of silica-rich minerals. 

The principal primary mineral groups are the silica minerals (including quartz), feldspars, feldspathoids, olivines, pyroxenes, amphiboles, and micas. All are silicates and can be classified structurally based on the arrangement of connected silica (Si04) tet-rahedra. Table 2.2 summarizes the classification system for these common rockforming minerals. 

Tectosilicates (framework) Continuous framework of tetrahedra, each sharing all four oxygens 1 2 Silica (e.g., quartz, Si02), feldspars [e.g., orthodase iqSiaAlOg)], feldspathoids... 

Microcrystalline feldspathoids and zeolites, both frame-work silicate structures, can precipitate from very alkaline solutions near 20 C at the expense of layer silicates, but true crystalline feldspars do not form at measurable rates in this way. 

Although feldspathoid structures are generally thought to be insufficiently porous to find widespread catalytic applications, the reactions of the occluded oxyanions are of catalytic interest. Previous work with other systems has shown that occlusion affects the properties of both the encapsulated species and the lattice itself (refs. 1,6,10,11). 

Olivine ((Mg,Fe)2Si04) and the feldspathoids (amphiboles, mainly ham-blende, and pyroxenes). In these minerals Fe(II) can be oxidized, increasing the weathering rate. 

The types of substance that are thermoluminescent, either in their natural state or after radiation bombardment, include (112) the alkali metal halides, calcite, dolomite, fluorite, aluminum oxide, magnesium oxide, gypsum, quartz, glass, feldspars, feldspathoids, certain dried clays, and ceramic materials. Of over 3000 rock samples examined for thermoluminescence, some 75% showed visible fight emission (112). Nearly all limestones and acid igneous rocks are naturally thermoluminescent, due mainly to the presence of trace elements of uranium, thorium, and so on. Calcium and magnesium... 

Schairer J.F, and Bowen N.L., 1935, Preliminary report on equilibrium relations between feldspathoids, alkali feldspars and silica. Trans, Amer. Geophys. I/ffion, 16th Ann, Meeting, pp. 325-328. 

The lower bound for the Al 2p binding energies for hydrothermally prepared f Al framework aluminosilicates is determined by the Loewenstein rule, which prohibits Al—O—Al bonding. This means that the Si/Al ratio must always be greater than 1.0. Thus, for zeolite Na—A and certain feldspathoids with this 1.0 Si/Al ratio, Al 2p is ca. 73.5 eV (Table VII) [37]. 

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