Optical sign

Optical signs of micas are negative, crystal system is monoclinic, and the streak is colorless. 

The optic sign of a crystal can be discovered by observing the effect... 

If a uniaxial convergent light figure is seen, the optical sign of the crystal may Tbe checked by the use of the quartz wedge in the manner described in the previous chapter. This is not necessary (except as confirmation) unless for any reason it is not possible to obtain actual measurements of both a> and e. 

Figure 4.31 Data for the characterization of an electrostatic lens, (a) Positions of the focal and principal planes (left-hand and right-hand sides are indicated by the subscripts Y and r respectively) and their distances (optical sign conventions are disregarded, i.e., the distances are described only by their lengths). (b) Geometrical construction applied to image the arrow ye by means of characteristic asymptotic trajectories, (c) Geometrical construction for an asymptotic ray with a pencil angle a,e. The shaded areas are needed for the derivation of the linear and angular magnification factors of the lens. For details see main text.

The surfaces seen on these photographs are known as ray velocity surfaces. For all uniaxial anisotropic crystals, we have a double surface when the crystal has a positive optic sign (like quartz), the ellipsoid of revolution is enclosed by the sphere, but if the crystal is optically negative (like calcite), the ellipsoid encloses the sphere. The assumption that the form of the variation of velocity for the extraordinary disturbance in uniaxial crystals is ellipsoidal was... 

We can now summarize the conclusions that have been reached for conditions of normal incidence about the light waves which pass through a general section of a uniaxial crystal. The two disturbances, ordinary and extraordinary, have parallel wave fronts but their velocities along the common wave normal direction are different if the optic sign is positive the ordinary waves travel faster, and vice versa. The two transmitted waves are linearly polarized. For the ordinary disturbance the vibration direction is perpendicular to the principal section... 

In the first supplement to the N.F. XIII identical refractive indexes, elongation and extinction data are given with the additional information that the optic sign... 

System Orthorhombic Crystal Habit Columnar Optical sign + Axial angle ... 

Optical Sign - Axial angle 0° Optic orientation (assigned acc. to crystal habit) ... 

System Orthorhombic Crystal Habit columnar Optical Sign - Axial Angle 69 Optic orientation (assigned acc.to crystal habit) XX c YY a ZZ b. Dispersion None observed Refractive Indexes a (w) = 1.517 (3 ( e) = 1.567 y = 1.592 Density 1.379 Refraction Experimental = 111.90 Calculated = 113.99. 

Po yo Space-groups optical sign. Colour Ref. Fluores- cence... 

Figure 4.11. Determination of optical sign by conoscopic examination with insertion of a compensator.

System orthorhombic Crystal Habit Tabular Optic Sign +... 

The directions and are the bisectors of the angles between the optical axes ri2 is the optical normal. The optical sign of the crystal is defined as follows (Fig, 4.24) ... 

We do not observe an image of the crystal in the focal plane of the objective of the microscope, but an interference pattern. Each point in this plane corresponds to the direction of a wave normal characterized by a birefringence, and hence, by an interference color or light intensity. The intensity goes to zero for all waves polarized according to the polarizer and the analyzer. The interference figures are characteristic of the crystal symmetry, the optical sign and the orientation of the indicatrix. 

All produets gave only levorotatory eompounds independently of the optical sign of the quartz used. Thus Pt-/-quartz eatalyst, based on quartz washed with HF, gave in dehydrogenation of butan-2-ol rotation of catalysate with optical rotations of -0.085° and -0.09° that went to zero in several tours after sedimentation of the suspension of quartz. In another experiment a rotation of -0.05 8°was obtained, but that disappeared in 4-5 hrs. The same (-)-rotation in solution was reeeived even from the suspension of crushed quartz or p5Tex glass and siliea. 

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