CRYSTAL STRUCTURES AND MINERAL PROPERTIES

Since the most important glass-forming systems are based on silicate compositions, the key crystalline components of glass-ceramics are therefore silicates. Certain oxide minerals, however, are important, both in controlling nucleation as well as forming accessory phases in the final product. 

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Zeolite, zeolite group A collective term for a family of aluminosilicate minerals characterized by framework structures that allow easy access and exchange of cations and small molecules (see chapter 2), The name derives from the Greek terms zein, meaning to boil, and lithos, meaning stone. The term is also applied to synthetic materials of comparable composition, crystal structure, and physical properties (see chapter 2). 

KYANITE. (Cyanite.) 3Al203-3Si02. This mineral has the same chemical composition as andalusite and sUlimanite, but differs in crystal structure and physical properties. Kyanite ore has a specific gravity of 3.5-3.7 and a variable hardness, 4—5 parallel to the long direction of its blades and 6-7 across them. 

Eujii T, Suzuki D, Gunjii K, Watanabe K, Moriyama H, Nishizawa K (2002) Nuclear field shift effect in the isotope exchange reaction of chromium(III) using a crown ether. J Phys Chem A 106 6911-6914 Gale JD (2001) Simulating the crystal structures and properties of ionic materials from interatomic potentials. Rev Mineral Geochem 42 37-62... 

Basso R. (1985). Crystal chemical and crystallographic properties of componnds with garnet or hydrogarnet structure. Neues Jahrb. Miner. Monat., 3 108-114. 

The discrepancy in numbers between natural and synthetic varieties is an expression of the usefulness of zeolitic materials in industry, a reflection of their unique physicochemical properties. The crystal chemistry of these aluminosilicates provides selective absorbtion and exchange of a remarkably wide range of molecules. Some zeolites have been called molecular sieves. This property is exploited in the purification and separation of various chemicals, such as in obtaining gasoline from crude petroleum, pollution control, or radioactive waste disposal (Mumpton, 1978). The synthesis of zeolites with a particular crystal structure, and thus specific absorbtion characteristics, has become very competitive (Fox, 1985). Small, often barely detectable, changes in composition and structure are now covered by patents. A brief review of the crystal chemistry of this mineral group illustrates their potential and introduces those that occur as fibers. 

Measurements of electronic absorption spectra in the visible region not only lead to the evaluation of CFSE s, but they also provide useful information about the crystal chemistry of transition metal ions in the crystal structures and causes of colour and pleochroism of minerals. In this chapter, techniques for measuring absorption spectra of minerals are briefly described and some general applications of the optical spectra to basic crystal chemical properties, such as colour and pleochroism, are discussed. These examples also amplify many of the features of crystal field spectra outlined in chapter 3. 

In the study of minerals and other geological materials, Raman spectroscopy has been applied for chemical analysis and in studies of molecular and crystal structure, and of elastic and thermodynamic properties. A particularly important field for the application of Raman spectroscopy in chemical analysis is in the study of fluid inclusions in minerals, where the Raman microprobe has been developed to enable nondestructive in... 

J. Arndt, W. Hummel, and I. Gonzalez-Cabeza, Displectic labradorite glass from the Manicouagan impact crater I. Physical properties, crystallization, structural and genetic implications. Phys. Chem. Minerals 8, j. 230—239 (1982). 

Manganese oxides, which have different structural and surface properties, vary substantially in their ability to promote the precipitation and crystallization of Fe oxides and oxyhydroxides. The Mn(II) dissolved from Mn oxides in the presence of Fe(II) also influences the crystallization of oxidation products of Fe(II). The Fe oxides formed as influenced by Mn oxides and dissolved Mn(II) range from lepidocrocite, goethite, maghemite, dkaganeite, feroxyhyte, magnetite, honessite-like minerals, to noncrystalline Fe oxides. Therefore, Mn oxides deserve close attention in the genesis of Fe oxides. 

Other theoretical methods. In addition to the procedure described above, three other theoretical methods have been developed for calculating fractionation factors involving minerals. The first is based on computer simulation of crystal structures and first principles prediction of their thermodynamic properties (Patel et al. 1991 Dove et al. 

Mineral A naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form, and physical properties. 

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