If you have no Malachite Gems (or only 1) you simply must wait and see if you can find/buy some Malachite Gems later on in the game ...

Tip:
if you wish to finish this quest, search your way to High Hall where you can find Beatrice and do a quest for her ! Then you can get 4 Malachite Gems in one time as reward for that quest wink

On 7th of february 2015 : I start a new adventure in the Divinity world of Original Sin,
it's a Fantastic Freaking Fabulous Funny ... it's my All Time Favorite One !