schlie·ren 
(shlîrən)
(shlîrən)pl.n.
1. Geology Irregular dark or light streaks in plutonic igneous rock that differ in composition from the principal mass.
2. 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.
[German, pl. of Schliere, from dialectal Shliere, streaks, from Middle High German slier, mud, slime, from Old High German sclierrun, pieces, bits.]