Snail shell creates blue iridescence with mineral
Mollusk uses calcium compound to shine, possibly as defense
![limpet](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2015/03/first_limpet.jpg?fit=860%2C460&ssl=1)
INTO THE BLUE The bright patterns on a hard-shelled mollusk may mimic those of a shell-free, poisonous snail.
Andy.Cowley/Wikimedia Commons (CC BY-SA 1.0)