Minerals birefringence

The disadvantage of this procedure is that the minerals maybe physically or chemically altered during burning. Eor example, the refractive index of clay minerals is changed the color, birefringence, and pleochroism of micas is altered carbonates are destroyed and the iron sulfides are oxidized to iron oxides. 

The optical character of chalcedony is distinct from that expected for the normally uniaxial mineral, quartz, and signals the fibrous nature of a particular sample. The direction of fiber elongation is often parallel to the [1120] crystallographic direction of the quartz structure (Fig. 2.19A), but other fiber directions have also been determined within a single sample (Frondel, 1985). The presence of helically twisted fibers are suspected from the variations in extinction and birefringence noted along the fiber length (Fig. 2.19C). More detailed information on the optical or other physical and chemical properties of quartz and its many varieties can be found in volume 3 of Palache et al. (1962) and in Frondel (1985). 

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

When either arsenolite or senarmontite is sublimed on to mica, it is deposited in oetahedra, respectively isotropic and birefringent, oriented so that similar dimensions of the crystal meshes coincide,8 for example -. As4Oe 13-54, Sb406 13-64, mica 13-66 A. Such orientation appears only to occur with minerals of ionic structure 9 and when both substances concerned have heteropolar linkings,10 so that the phenomenon is said to provide evidence of this type of linking. 

If the birefringence is low as in asbestos minerals, or if the particle is thin, the color seen will be a low order white or gray. A retardation plate or compensator added to the optical path can add or subtract retardation. Whether retardation is added or subtracted depends upon whether the slow ray of the com-... 

If the slow ray of the compensator is parallel to the slow ray of the particle, the retardation of the compensator will be added to the retardation of the particle and a higher order retardation color will result. If the slow ray of the compensator is perpendicular to the slow ray of the particle, subtraction of retardation will occur and a lower order retardation color will result. With asbestos minerals, or other minerals having low birefringence, the two colors seen will be first order yellow with the slow ray of the asbestos perpendicular to the slow ray of the compensator and second order blue with the slow ray of the asbestos parallel to the slow ray of the compensator if the compensator has 550 nm of retardation, i.e. first order red. 

Palmer DC (1994) Stuffed derivatives of the silica polymorphs. Rev Mineral 29 83-122 Palmer DC, Bismayer U, Salje EKH (1990) Phase transitions in leucite order parameter behavior and the Landau potential deduced from Raman spectroscopy and birefringence studies. Phys Chem Minerals 17 259-265... 

When mounted in mineral oil ana examined by means of a polarizing microscope, propionyl erythromycin lauryl sulfate exhibits birefringence and extinction positions when the microscope stage is revolved. ... 

Flexibihty of the moieties is another important parameter because it was recently shown that flexible objects require larger volume fractions to undergo nematic ordering. Flexibihty also reduces the nematic order parameter at the transition. Intuitively, very flexible mineral polymers should not show any orientational order at rest, but may display a strong flow birefringence. Thus, any soluble system where the structural unit in the solid state is anisotropic may not necessarily be a lyotropic Hquid crystal. For example, in solution a polymer is much less constrained than in the soHd state, and hence one must consider the elastic properties of the polymer chain and whether the anisotropic units still exist in solution. As shown recently for the case of the complex fluid with a min-... 

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