Spinel is a mineral (magnesium aluminate) that creates optically clear objects and is so much tougher, stronger, harder than glass that doesn't get scratched in a sand storm and won't break as easily as glass. Ok, ok it's very hard (and expensive) to polish, so if not lenses, maybe we can dream of some clear filters made of it in the future. Read more at the NRL page:
http://www.nrl.navy.mil/media/news-releases/2015/transparent-armor-from-nrl-spinel-could-also-ruggedize-your-smart-phone
http://www.nrl.navy.mil/media/news-releases/2015/transparent-armor-from-nrl-spinel-could-also-ruggedize-your-smart-phone