Over two decades have passed since it helped usher in the grunge era, but Pearl Jam’s “Ten” has finally sold 10 million copies. The hard rock group that’s attracted fans and music critics by adhering to a strict guideline of artistic integrity now joins major acts including Britney Spears and the Backstreet Boys in the so-called Diamond-selling status.

“Ten,” Pearl Jam’s debut album, is the 22nd album to sell 10 million copies since 1991, when Nielsen SoundScan began tabulating data, as noted by USA Today. The record sold 4,000 copies in the week ending Feb. 17, surpassing the mark of 10 million sold in the United States.

“I’m happily shocked to hear that. Wow,” guitarist Mike McCready told Billboard. “We had no idea that it was ever going to do that well. I just felt like it was a really cool record and that I was in a good band.”

Any music fan who has turned on hard rock radio in the past two decades is almost certainly familiar with the landmark record. “Even Flow,” “Jeremy,” and “Alive” have all become staples on the airwaves because of swirling, Hendrix-style guitars and Eddie Vedder’s signature bellow.

“Ten” joins Usher’s “Confessions,” Linkin Park’s “Hybrid Theory” and Adele’s “21” among the four albums to break 10 million sales since the start of 2012. The top-selling album since SoundScan began in 1991 is Metallica’s self-titled 1991 album, with 15.86 million copies sold, followed by Shania Twain’s “Come On Over,” with 15.53 million, then “Jagged Little Pill” by Alanis Morissette at 14.82 million.

Unlike other so-called grunge bands like Nirvana and Soundgarden, Pearl Jam has not only endured but arguably reached greater musical achievement than its debut album may have suggested. The group is currently working on a new record, its first since 2009’s “Backspacer,” and has scheduled concert dates for summer 2013.

The band’s genesis was even less likely than the success Pearl Jam has achieved, though. The roots of the band can be found in Mother Love Bone, a similar heavy rock group that sought a new singer after the death of vocalist Andrew Wood. A tape of instrumental songs the group was working on after Wood’s death eventually made its way to Vedder, who was working in a gas station at the time and thought up the lyrics to much of “Ten” during a surfing trip.