This reminds me about the Scaly-foot gastropod[1] mollusc which "possesses a trilayered structure comprised of a mineralized iron sulfide–based outer layer (OL)

This reminds me about the Scaly-foot gastropod[1] mollusc which "possesses a trilayered structure comprised of a mineralized iron sulfide–based outer layer (OL) containing greigite..."[2] [1] https://en.wikipedia.org/wiki/Scaly-foot_gastropod https://en.wikipedia.org/wiki/Scaly-foot_gastropod [2] http://www.pnas.org/content/107/3/987 http://www.pnas.org/content/107/3/987