streak

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streak

1. 
a. (of lightning) a sudden flash
b. (as modifier): streak lightning
2. Mineralogy the powdery mark made by a mineral when rubbed on a hard or rough surface: its colour is an important distinguishing characteristic
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

streak

[strēk]
(mineralogy)
The color of a powdered mineral, obtained by rubbing the mineral on a streak plate.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.