I recommend you to check l2wiki.com (http://l2wiki.com/) for exact information on how many crystal you will get when your enchant fails.
There is a Crystallization table for every item registered in that database.
(Search for the exact item as bound and standard items give different ammount.)
If you want crystal be sure to check which is the best way to get the most income.
For example:
you get 1590 r-cry from a +3 bound apocalypse weapon with crystallization,
if it break through +4 you gain 1545,
however if you crystallize at +4 it gives 2590 r-cry (1.000 more than at +3)