i can barely get agates to spark period.....i even bought pretty pricey german agates....they just arent that sharp.....and i dont think you can knapp them....you can "sharpen" them with a diamond file i do believe....but i think the way they are machine cut and everything they cant be knapped like an english flint.....i use nothing but english flint....if i have a misfire its because of me....not my flint...not cleaning up after a few shots or oil on the flint or frizzen ect......but if everythings clean and oil free my flints spark great......i dont even try to knapp mine.....i just cant figure it out....i can get it to work somewhat better after it dulls...but it doesnt last long.....i keep all the worn ones for when i do get around to learning to knapp......till then i have 2 supplies of black english flints i get to hand pick out of 1000s.....im taking my lock with me when i go soon and getting ones that fit perfectly.....i carry a bunch while hunting...im prepared for the worst....ive had flints pretty much explode on impact....had them crack.....chip really bad ect.......one was waht i thought to be a PERFECT black english flint.....got it all in there aligned perfectly....when to fire it at the end of the day and it blew up....gun went off like a champ.....but the flint was in pieces after that.....dont know what happens every once in a while....guess the grain and eveything could been wrong........or it could been my old frizzen...i had a regular tc frizzen on my hawken last year and flints didnt last long at all.....and sparks werent good....there were many grooves in my frizzen....so i fit a lyman frizzen to the lock.....and it works great......and i havent changed my flint in about 50 shots or so.........