rock flour

American  

noun

1. glacial meal.

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rock flour British  

noun

1. 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

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Etymology

Origin of rock flour

First recorded in 1880–85

Example Sentences

Such a fault would lack the “rock flour” that builds up in active faults as they grind away and makes it hard to discern how an individual earthquake divides its energy into seismic waves, heat, strain, and pulverizing rock.

From Science Magazine

Rock flour turns the water milky-white as it rushes along its bed.

From Seattle Times

He is exploring the possibility of marketing rock flour — the fine powder created by glacial erosion — as a source of nutrients and neutralizing agents for tropical soils.

From Nature

Where the margin lay upon the lands numerous streams issued from beneath the ice, milk-white with rock flour, and built up great outwash plains and valley trains of gravel and sand.

From Project Gutenberg

And though by ship you can float close to a mountain’s foot, you can’t see the jewels hidden in its crags: valley lakes turned Technicolor, tinged a glowing green from “rock flour,” the ground-up minerals that pour from the meltwater of a glacier and hang suspended in the lake.

From New York Times