Appropriately named, armor stones are large, extremely hard boulders selectively placed to protect land from the natural, damaging forces of water. Armor stones are used on shorelines and banks to resist erosion due to the action of large waves. These stones can be seen on jetties in majors rivers, coastal shores and along the downwind shores of large lakes.
A limestone ledge is selected to produce armor stones because of its proven durability. Boulders weighing two to eight tons are removed from the quarry pit by a crane or front end loader. When large quantities of armor stones are required, special blasting techniques are used to provide more large sized stones. Transportation and placement of the stones is a special concern due to the size of each individual stone.
Specifications for armor stone are found in section 4130 of the Iowa Department of Transportation, English Standard Specifications for Highway and Bridge Construction.