a construction worker operates a large rock crusher machine that breaks down big stones. The machine's powerful jaws grip a boulder and crush it with tremendous force. Large rocks go into the top of the machine and come out as fine gravel and dust at the bottom. Clouds of dust particles float in the air around the crushing mechanism. Other workers nearby cover their faces from the fine powder being created. A pile of crushed stone powder accumulates below the machine's output chute. materials being reduced to fine particles by crushing and grinding