if what i've observed is correct, digging experience weighs heavily on random factors. i can post more later, after a day or two of actually paying attention to exp. points and what i dig up. but here's a general idea. i'm a lvl 18 digger with 18 iq and 58 luck (1 in the rest). and i can get all the gems now. i pick up 1 to almost 40 of iron, copper, and tin. up to around 5 lapis, opal, pearl, ruby, emerald. 1 or 2 diamonds (split roughly 50/50). and 1 dispro, kith, centro, and the odd hyp (will get more when i get to 60 luck next lvl). and i believe i get successful digs around 7 or 8 out of every 10 tries. but i know you're asking about exp. from what i can remember, i get anywhere from 80-160 points per successful dig (i may be a bit off on those values). and it doesn't seem to matter (much) what i dig or how many i dig up. i've gotten high xp's for 1 copper, and low xp's for 35 copper. the higher gems seem to average slightly higher xp's than the lower stuff, but that could just be psycological. (if there is a difference, it isn't much). maybe i'll store up clicks on my digger for a few days, and take some notes.