Coquina, the stone that absorbs cannon balls
July 11, 2019 11:25 AM Subscribe
Coquina (Wikipedia) is a sedimentary rock that is composed of fragments of invertebrate shells, and it has been used as a building stone in Florida for over 400 years. At a distance, it might appear like a coarse sandstone, and it is very porous, requiring extensive preparation to use as a building material, such as in Castillo de San Marcos (YouTube clip). But its porousness can be a benefit, as seen in The Mystery of Florida's Cannonball-Eating Spanish Fort (Atlas Obscura), where coquina behaves very differently when struck by cannonballs or bullets. The material was studied recently, and here's the full report on The Impact Response of Coquina: Unlocking the Mystery Behind the Endurance of the Oldest Fort in the United States (Journal of Dynamic Behavior of Materials).