Promotions for free Facebook Credits are suddenly mushrooming. In the latest one, Facebook partner Rixty is giving away bonus credits at Coinstar machines in the U.S.

In the promotion, running from today until September 7, non-Rixty customers will get 10 free Facebook Credits just for converting their spare change to cash at a participating Coinstar machine.

For existing Rixty customers, the company is offering an even bigger bonus, when they buy Facebook Credits at a Coinstar machine.

- Spend $5 to $50: Get 15 BONUS CREDITS
- Spend more than $50: Get 35 BONUS CREDITS
- Spend more than $100: Get 70 BONUS CREDITS
- Spend more than $150: Get 105 BONUS CREDITS

In a blog post, Rixty chief executive Ted Sorom said: “Most everyone has a coin jar at home. Additionally, statistics show that over 20% of US households lack credit cards, so we’re excited to be able to provide the millions of cash spending users the opportunity to quickly and easily visit one of Coinstar’s many convenient locations and turn in their cash and coins for online purchasing power.”

Facebook Credits, the common currency for buying virtual goods in games on Facebook, has had a lot of marketing juice lately. Since July Facebook has been giving away Credits directly to users. Meanwhile, PayNearMe is running a promotion for customers who buy Credits at 7-Eleven stores.

Facebook receives 30% of any transaction made with Credits on its site and social gaming is a growing revenue source for the company. Last week the company advertised a position for a head of games partnerships.