Extinction undulatory

Optically undeformed or weakly deformed [ [ Strong undulatory extinction... 

Undulatory extinction Optically undeformed Inclusion array at midplane Microcrack... 

The trace of the planar central zone of the microcrack-ladder is marked by the presence of negative crystals and inclusions. This characteristic indicates that microcrack-ladders must be related to healed longitudinal fractures. The formation of unhealed microcracks normal to the loading direction (i.e., the rungs of the ladders) can be understood as follows. Undulatory extinction and dislocation microstructures observed within the microcrack-ladders indicate that plasticity is restricted to a narrow zone ( 100 / m wide) within the otherwise-undeformed host crystal. Therefore, the host crystal responded elastically while the load was applied the elastic strain A/// being about 0.5 percent. Now, in the plastic zone of the... 

Cataclastically deformed plagioclase could be formed near the surface of the Moon and asteroids during heavy bombardment by meteoroids. An example of fractured plagioclase is observed in the eucrite Yamato (Y)-792510 (Fig. 7.3) consisting mainly of plagioclase and pyroxene which show undulatory extinction. Compared with pyroxene, plagioclase grains are heavily fractured. 

A single crystal should ideally appear either uniformly dark, irrespective of position, or else undergo a sharp change in appearance from uniformly dark to uniformly bright every 90°. Undulatory extinction is indicative of strain in the crystal lattice. A composite crystal, i.e., an intergrowth of two or more crystals, will often show light and dark simultaneously. A twin is a composite of two crystals joined symmetrically about a twin axis, or a twin plane, and often appears as a V, L, or + shape (20). 

In cross-polarized light, rotate the stage 45 from crystal extinction (darkness) as illustrated in Photograph 6-2. For crystals that exhibit a strongly wavy (undulatory) extinction, birefringence data may be questionable. Therefore, crystals with uniform or nearly uniform extinction are sought. 

The undulatory extinction of strained quartz has become important in engineering geology as it serves as an indicator for aggregates to undergo Alkali-Silica Reaction (ASR). The amount of strained quartz found in the rock samples varied between 18 and 50% and their respective undulatory extinction angle varied from 16° to 36° Table 3. 

The crossed-polarizer image of a cytoplasmic extract shows Si02 replacements in grey and white arrangements, with undulatory extinction. 

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