14th April 2011 Crystal Eyes

Some species of chiton, which is a mollusk, have eyes make of rock crystal. Their shells are also make of this. With these eyes, which are located in their shells, they can distinguish between a possible threat and a the natural dimming of light.  Their vision is probably around a thousand times coarser than human vision.

For them, protein eyes like we have would quickly be worn away.

http://news.nationalgeographic.com/news/2011/04/110414-eyes-rock-crystal-mineral-chiton-mollusk-vision-animals-science/

http://blogs.discovermagazine.com/notrocketscience/2011/04/14/chitons-see-with-eyes-made-of-rock/