rock flour


1880–85 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
rock flour
very finely powdered rock, produced when rocks are ground together (as along the faces of a moving fault or during the motion of glaciers) and are thus chemically unweathered

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Example sentences
The glaciers in the background grind the rocks underneath as they melt in the
  summer and produce rock flour.
We also learned the secret of the mountain lakes' brilliant turquoise color: a
  substance called rock flour.
It is found beneath old swamps, as mud on the bottom of the sea, and as the
  ground-up rock flour left by melting glaciers.
Rock debris is crushed and ground into fine grains, called rock flour.
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