Armor Stone

Armor stone is large, heavy chunks of quarried rock used to shield shorelines, streambanks, and bridge piers from moving water. Each piece usually weighs anywhere from 200 pounds up to several tons. The blocks are angular and blocky, so they interlock when stacked and stay put under wave hits and fast current.

"Armor stone" describes a size class. The rock itself can be granite, limestone, or hard sandstone, and pieces are sized by individual weight instead of a sieve number. Classes like R-3 through R-8, or "Class I through IV" in USACE specs, tell you the target median weight of each block, from a few hundred pounds up to 6 tons or more. Expect to pay $60 to $150 per ton at the quarry, plus freight, because the pieces are too big for a standard dump truck and often need a loader on site.