What's left --

--of a piece of 270 million year old gneiss after its been rolling around in the Aliakmon River for who knows how long.

This cobble of lineated gneiss has weathered so that each feldspar grain stands out on the surface, and the "softer" mafic minerals weather away around them. The result looks like petrified rice. Each white grain is about 0.5 cm long.