Electronic Arts subsidiary PopCap has launched an open beta for Lucky Gem Casino, its fourth release on Facebook and an original title allowing users to gamble with virtual currency.

The burgeoning casino-themed social game space has seen plenty of activity in recent months, with virtual gambling game company IGT buying Double Down Interactive (DoubleDown Casino) for $500 million, and Caesars Interactive Entertainment acquiring Playtika (Slotomania) and releasing Caesars Casino.

Social game giant Zynga is also preparing to jump into the market with its own Zynga Casino franchise, which will include its popular Zynga Poker/Texas HoldEm Poker game (33.2 million monthly active users, according to tracking site AppData) and its upcoming Zynga Bingo.

"Casino-themed social games are one of the fastest growing genres on Facebook," says PopCap's worldwide publishing VP Dennis Ryan. The company's Lucky Gem Casino attempts to crack the space by featuring images and characters from the developer's other popular titles like Bejeweled and Zuma.

To avoid breaking any laws that restrict online gambling in the U.S., Lucky Gem Casino's seven free-to-play games allow players to purchase and win only Facebook Credits -- the social network's universal virtual currency -- which they cannot redeem for real cash.

This marks the fourth social game PopCap has released on Facebook, after Bejeweled Blitz (10.1 million monthly players), Zuma Blitz (2.7 million monthly players), and Pig Up (debuted in June, currently unavailable on Facebook). The company will launchSolitaire Blitz next month, too.