Stone axe, adze 100 primitive trick for quick grinding testing on hard wood glass

2014 04 05 Quickly and prehistorically crafting a stone adze (at least the cutting edge; from a pebble ) In 2011, I made a try and it took me 5 hours to create a cutting edge on a smooth stone and 3 more hours to sharpen it. Yesterday, it took me only 2 hours on another pebble I made a quick comparison : the 2 pebbles have the same ( ) hardness : at least both are harder than the glass of a beer bottle. And this bottle is harder than the steel of a knife. Possible explanations : the