Benji Madden gave Cameron Diaz a $25,000 black opal.

The 35-year-old rocker reportedly missed the 'Sex Tape' actress so much while he was touring Australia recently that he splashed out on the rare gemstone to show her how much she means to him.

A source said: ''Cam thinks the opal is the most beautiful thing she's ever seen. She absolutely loves it.''

The former Good Charlotte star decided to pick up the gift, which was sourced from an Australian mine, after being ''amazed'' at how the ''deep-blue stone matched her eyes.''

The couple got together in May after being introduced by Nicole Richie, who is married to Benji's twin brother Joel Madden.

Asked if she set them up, she previously said: ''Yes. I'm going to take responsibility for everything!''

A source previously claimed they quietly got engaged recently and are planning to marry in the Napa Valley, California in the near future.

However, Cameron, 42, recently insisted: ''I'm not looking for a husband or marriage or not not looking for that stuff. I'm living, not thinking what I should or shouldn't be doing with my life.''