Natural stone is tumbled to artificially age stone.  The result is that the sharp edges of the stone are rounded and smoothed off.  Any riven is also smoothed off.   Another consequence of tumbling is that the surafce of the natural stone actually becomes less porous which helps to make it more resistant to staining and therefore low maintenence.  Off course tumbling can take place naturally as well, just look at reclaimed Yorkstone which has in effect being tumbled by people, cars and weather over the best part of 100 years.  Who can wait 100 years though.  Check out our tumbled interior Jura limestone tiles