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Experiment
Coquina Rock Weathering Test
Test how coquina — the shell-rock old forts were built from — weathers.
1 week (5 min setup, observe daily) Easy
📋 What You'll Need
- •2 small coquina pieces (found on a beach) OR shell fragments
- •2 small regular rocks of similar size
- •2 cups of water
- •Salt (3 tablespoons)
- •An old toothbrush
👣 Step by Step
🔍 What to Observe
- •Which rock eroded more in saltwater?
- •Did the coquina get softer at the edges?
- •Why might early Spanish builders have chosen coquina for forts?
💡 Tips & Safety
- •Coquina is made of tiny broken shells compressed together — it's softer than granite.
- •Castillo de San Marcos in St. Augustine is built of coquina — it absorbed cannonballs!
- •Don't use rocks bigger than a golf ball so they fit in the cups.