on block form of cobblestone:
chance of 100%:
set event-block to diamond ore
stop
chance of 10%:
set event-block to gold ore
stop
chance of 15%:
set event-block to iron ore
stop
chance of 40%:
set event-block to coal ore
stop
chance of 1%:
set event-block to emerald ore
stop
chance of 8%:
set event-block to quartz ore
stop