Mollusk uses calcium compound to shine, possibly as defense
Taking a trick from birds and butterflies, a mollusk shines blue using intricate structures that allow selective reflection of light. But unlike other animals, the blue-rayed limpet, a snail that lives along the rocky shores of the northeastern Atlantic, creates functional iridescence using a hard mineral rather than an organic molecule such as a protein.
The shell of the blue-rayed limpet, Patella pellucida, is largely made of calcium carbonate platelets. Just beneath the shell's surface, materials scientist Ling Li of Harvard University and his colleagues found two distinct microscopic arrangements of the mineral: a zigzag structure that reflects blue light and a layer of spherical particles that absorbs the rest of the light, rendering the blue brilliant.