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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.

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

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.

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.

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.