rock flour
Extremely fine-grained sediment produced by the grinding of bedrock beneath a glacier — particles of silt and clay so small they stay suspended in water, giving glacial meltwater streams their distinctive milky, turquoise, or gray-green color. Rock flour is the powder that results from stone being crushed between two moving surfaces — the glacier and the earth.
Etymology
Descriptive English compound. The rock has been ground to flour.
Notes
The extraordinary blue-green color of glacial lakes — Lake Louise, Moraine Lake, Peyto Lake — is caused by rock flour suspended in the water, which scatters light.
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