Scientists create gold nuggets that are 98 percent air
 

Researchers at ETH Zurich have accomplished a bit of modern-day alchemy, transforming 20 carat gold into a lightweight foam. Well, technically it's an aerogel: an exceedingly light and porous matrix of material. It's so porous, in fact, that the foam...

http://www.engadget.com/2015/11/26/s...8-percent-air/