Coquina, the stone that absorbs cannon balls

July 11, 2019 11:25 AM

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).
posted by filthy light thief (18 comments total)

I live down the street from the Castillo and this post is EXTREMELY relevant to my interests.
posted by saladin at 11:27 AM on July 11, 2019 [7 favorites]

But NOT because I'm planning a daring raid on the fort. Not at all.
posted by saladin at 11:35 AM on July 11, 2019 [21 favorites]

One of the few things I miss about south Florida, in addition to the delicious tacos, is all the coquina. It's just a really neat material.
posted by tobascodagama at 12:14 PM on July 11, 2019

Also, here's another cool hunk of coquina in town.
posted by saladin at 12:19 PM on July 11, 2019 [1 favorite]

This is super cool. I remember wishing for more info about how coquina worked when visiting the Castillo many years ago, and yay! New experiments on an old substance. (And when we're talking about a 300-year-old structure, a 2015 journal article totally still counts as new.)
posted by asperity at 12:29 PM on July 11, 2019

Super cool -- is there a link to the video of those ball impact experiments in Figure 10?

I can't believe I can't find a Youtube video of someone shooting a cannonball into a block of coquina -- this seems like something that would be perfect for someone like the Hydraulic Press Channel or Smarter Every Day.
posted by This_Will_Be_Good at 1:26 PM on July 11, 2019 [1 favorite]

What I do not like is the concrete with white seashell detrius pushed into it as a faux-coquina facade. That is all.
posted by RolandOfEld at 1:38 PM on July 11, 2019 [3 favorites]

This is referenced in the wikipedia link, but as a Floridian (west coast) it's also the name of just the darn cutest little bivalves you ever did see, available in a startling spectrum of colors and adorable to watch dig their eentsy selves under the surface of the sand.
posted by penduluum at 2:00 PM on July 11, 2019 [5 favorites]

And they're apparently tasty (via Minorcan Food of Florida, the only other post to mention coquina).
posted by filthy light thief at 2:02 PM on July 11, 2019 [1 favorite]

Oh, hey, I remember those little bivalves from east coast beach vacation, I did not know they were called coquinas, we just thought of them as little mussel-y things.
posted by tavella at 2:30 PM on July 11, 2019 [1 favorite]

thanks to pendulum, I remembered that I first saw the word coquina not with anything construction related, but on a seafood restaurant menu.
posted by numaner at 3:30 PM on July 11, 2019 [1 favorite]

Ha, I've made coquina broth before. We were staying at a hotel in Daytona Beach, and there were massive piles of the things washing up. We scooped up a bucketful and brought them back to the room. After we boiled them there were little clam-corpses floating around and I felt kind of like the Walrus. But mixed with vodka it made a good cocktail.
posted by RobotVoodooPower at 4:35 PM on July 11, 2019

Also, here's another cool hunk of coquina in town.

Huh, so that's why highway 90 alt is called Old Spanish Trail in south Houston. Back in the days of the 55mph speed limit, it was the scenic route across Texas. Houston has the same problem of no available building stone, just sand and clay. The oldest buildings are all made from brick.
posted by Bee'sWing at 4:52 PM on July 11, 2019 [1 favorite]

Oh, and coquina can be used for sculpting.
posted by RobotVoodooPower at 5:05 PM on July 11, 2019 [1 favorite]

I grew up digging holes at the beach to catch coquina. Super fun to watch them dig back in the sand in between waves. There’s cool coquina buildings all over the state. There’s several houses in my neighborhood made of coquina brick. The fort in St Augustine has stood for nearly 500 years and still looks great inside and out. Coquina really is an amazing material.
posted by photoslob at 5:49 PM on July 11, 2019 [1 favorite]

The fort in St Augustine has stood for nearly 500 years and still looks great inside and out. Coquina really is an amazing material.

I googled for coquina and Florida Man. Nothing except some flesh-eating bacteria, which has nothing to do with the rock.

It survived Florida Man. Coquina really is an amazing material.
posted by saysthis at 6:31 PM on July 11, 2019

This is one of those posts were you rifle through places to find a photo.

SOMEWHERE.

Yes yes, well preserved fort....but can *it* eat Ripley's ™®© if said shot were applied with abraded trilobites, brachiopods, etc.
posted by clavdivs at 7:42 PM on July 11, 2019

Nobody:

Person owning a chunk of coquina: "Heyyyyy, my coquina!"
posted by turbid dahlia at 9:16 PM on July 11, 2019