I would classify the destruction of the item as a Chaotic Good act. That doesn't change your alignment, nor do I think it should threaten your Paladinhood.
However, your actions were a direct result of your character's greed. I can, to a certain extent, see the top of the paladin slide (with blackguard at the bottom).
But as Artoomis pointed out, all is not lost. Seek out your church, atone, and maybe see if your GM will work with you on an item like the Phylactery of Faithfulness that will let you know if an action you are considering would violate your Paladin code. Also, talk to the GM (calmly) and find out what his reasoning behind the decision was. Don't whine, threaten, or belittle. Be an adult (even if he won't). You'd be surprised at the sheer number of problems that can be solved by that.
If all else fails and your paladin is on the fast track to hell, then enjoy it. Start murdering peasants. Like that blacksmith in the last town, you know he cheated you a few copper coins when he re-shod your horse. Or how about those town guard that wouldn't let you enter town without peace-bonding your weapons? I bet they wouldn't be so hasty to strike at you when you have a few orphans strapped to your armor.
Be evil, you know you want to.