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