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Irregular dark or light streaks in plutonic igneous rock that differ in composition from the principal mass.

Regions of a transparent medium, as of a flowing gas, that are visible because their densities are different from that of the bulk of the medium.

In petrography, streaks or irregularly shaped portions of an igneous rock which differ in texture or composition from the main mass.

Regions of a fluid having different refractive index because of their different density

Irregular streaks of different composition in some igneous rocks