Mineral anisotropic

Furukawa N, Sato S (1999) New Aspects of Hypervalent Organosulfur Compounds. 205 89-129 Gabriel J-C P, Davidson P (2003) Mineral Liquid Crystals from Self-Assembly of Anisotropic Nanosystems. 226 119-172... 

The light incident on a mineral surface divides itself in a number of ways. It is partly reflected, partly transmitted, and partly absorbed. Minerals exhibiting metallic bonding have a high reflectivity. Those characterized by ionic or covalent bonding have a high transmissivity. The optical properties are anisotropic they are different in different directions and depend on the arrangement of atoms in the crystals. 

The parent materials differ from each other in many aspects the differences are being related both to their origin (coal or pitch) and heat treatment temperature. Clearly, coal should be classified as a polymeric type precursor while the others, such as carbonaceous precursors of relatively low, except for AC, carbonization degree. Specific of pitch-derived materials is distinctly lower mineral matter and heteroatoms content. Anisotropic appearance with predominating flow type texture proves the superior extent of structural ordering in pitch-derived materials. 

Archibald, D.D. and Mann S. (1993) Template mineralization of self-assembled anisotropic lipid microstructures. Nature,... 

Most minerals polarise light that passes through them, i. e. show anisotropic behaviour Birefringence-the maximum difference between the refractive indices of a mineral... 

If the diffusion medium is isotropic in terms of diffusion, meaning that diffusion coefficient does not depend on direction in the medium, it is called diffusion in an isotropic medium. Otherwise, it is referred to as diffusion in an anisotropic medium. Isotropic diffusion medium includes gas, liquid (such as aqueous solution and silicate melts), glass, and crystalline phases with isometric symmetry (such as spinel and garnet). Anisotropic diffusion medium includes crystalline phases with lower than isometric symmetry. That is, most minerals are diffu-sionally anisotropic. An isotropic medium in terms of diffusion may not be an isotropic medium in terms of other properties. For example, cubic crystals are not isotropic in terms of elastic properties. The diffusion equations that have been presented so far (Equations 3-7 to 3-10) are all for isotropic diffusion medium. 

In an isotropic medium, D is a scalar, which may be constant or dependent on time, space coordinates, and/or concentration. In anisotropic media (such as crystals other than cubic symmetry, i.e., most minerals), however, diffusivity also depends on the diffusion direction. The diffusivity in an anisotropic medium is a second-rank symmetric tensor D that can be represented by a 3 x 3 matrix (Equation 3-25a). The tensor is called the diffusivity tensor. Diffusivity along any given direction can be calculated from the diffusivity tensor (Equation 3-25b). Each element in the tensor may be constant, or dependent on time, space coordinates and/or concentration. 

Most diffusion processes encountered in Earth sciences are, strictly speaking, multicomponent diffusion. For example, even "self "-diffusion of oxygen isotopes from an 0-enriched hydrothermal fluid into a mineral is likely due to chemical diffusion of H2O into the mineral (see Section 3.3.3). Because a natural melt contains at least five major components and many trace components, diffusion in nature is complicated to treat. For multicomponent and anisotropic minerals,... 

For minerals, if diffusion is anisotropic, the bulk method gives only an average diffusivity for an assumed effective shape, but cannot determine the diffusivity along different crystallographic directions. The profiling method is necessary to quantitatively resolve the anisotropy. 

Example 4.1. Suppose olivine and garnet are in contact and olivine is on the left-hand side (x<0). Ignore the anisotropic diffusion effect in olivine. Suppose Fe-Mg interdiffusion between the two minerals may be treated as one dimensional. Assume olivine is a binary solid solution between fayalite and forsterite, and garnet is a binary solid solution between almandine and pyrope. Hence, Cpe + CMg= 1 for both phases, where C is mole fraction. Let initial Fe/(Fe- -Mg) = 0.12 in olivine and 0.2 in garnet. Let Xq = (Fe/Mg)gt/ (Fe/Mg)oi = 3, >Fe-Mg,oi = 10 ° mm+s, and Dpe-Mg,gt =... 

In many luminescence centers the intensity is a function of a specific orientation in relation to the crystallographic directions in the mineral. Even if a center consists of one atom or ion, such luminescence anisotropy may be produced by a compensating impurity or an intrinsic defect. In the case of cubic crystals this fact does not disrupt optical isotropy since anisotropic centers are oriented statistically uniformly over different crystallographic directions. However, in excitation of luminescence by polarized fight the hidden anisotropy may be revealed and the orientation of centers can be determined. 

E. 1. Givargizov, Highly Anisotropic Crystals, Dordrecht, D. Reidel, 1986 1. Sunagawa (ed.j. Morphology of Crystals, Parts A and B, Dordrecht, D. Reidel, 1987 1. Sunagawa (ed.). Morphology of Crystals, Part C, Dordrecht, D. Reidel, 1994 1. Rostov and R. 1. Rostov, Crystal Habits of Minerals, Sofia, Professor Martin Drinov Academic Publishing House and Pensoft... 

The coefficents of thermal expansion of mineral fillers are considerably less than those of thermoplastic polymers and thus their incorporation can significantly reduce that of a composite material. This is a generally useful effect. High aspect ratio fillers, when aligned by processing, will often give rise to anisotropic effects, leading to problems of warp age [69]. 

The refractive index is the most important optical property and its effect in determining the appearance of the polymer composite has already been referred to above. Amorphous fillers such as glass fibres and beads have only one refractive index, but most mineral fillers are crystalline and have anisotropic crystal structures resulting in a number of different indices, and this can cause complex and undesirable interference effects [27]. 

Anyone who has seen the well-formed crystals of minerals in our museums must have been impressed by the great variety of shapes exhibited cubes and octahedra, prisms of various kinds, pyramids and double pyramids, flat plates of various shapes, rhombohedra and other less symmetrical parallelepipeda, and many other shapes less easy to describe in a word or two. These crystal shapes are extremely fascinating in themselves artists (notably Durer) have used crystal shapes for formal or symbolic purposes, while many a natural philosopher has been drawn to the attempt to understand first of all the geometry of crystal shapes considered simply as solid figures, and then the manner in which these shapes are formed by the anisotropic growth of atomic and molecular space-patterns. 

Carbon form microscopically distinguishable carbonaceous textural components of coal and coke, exuding mineral carbonates recognized by reflectance, anisotropy, and morphology derived from the organic portion of coal and can be anisotropic or isotropic (ASTM D-5061). 

---