You know when you hear a new classic. There's a shadow cast over anything you've heard before. Crack the Skye is the monolith that can do that to any recent metal you may have admired.

With producer Brendan O' Brien (Bruce Springsteen, Rage Against the Machine, Pearl Jam), Mastodon has crafted a 21st century holy grail of progressive metal. "Ghost of Karelia" takes you on a flight to space and the space between spaces. "The Last Baron" is a melancholy trip through psychedlic territory, shimmering with motorcycle riffage. The title track begins as what seems to be a heavy offering then blooms into a beautifully arranged and smartly produced piece.

Crack the Skye is the watershed moment in a band's career that grants tenure in the halls of a genre while giving license to break the genre's formula. This is a heavy metal album but also progressive. At some moments, it's a pop album. Other times it transgresses description and establishes what can only be labeled "Mastodon-ian."

This album is a rich tapestry of influences and that is why it is so great in only seven tracks. Mastodon has taken everything they've ever heard and loved and made it their own, not just re-inventing themselves but actually establishing the band's name.

It usually takes some time for a new album to sink in and be accepted as a part of the band's legacy but this album instantly branded itself as not only being of Mastodon but as canon for metal and, time will tell, 21st century music.

It's a different album from previous releases, however. Big fans of Leviathan may need to brace themselves for more craft and less thrash. Blood Mountain disciples will make an easier transition but will notice the marked shift from speed to groove.

For Mastodon, this album should propel them into the stratosphere of timelessness but for long-time fans, this may be a time to raise eyebrows. There are less drum fills, less shred-feasting and less yelling (although a guest appearance from Scott Kelly of Neurosis reminds us of the band's roots).

So don't expect the Mastodon of 2004 or 2006. This is an album forged from experience and emotion, and is therefore unique among the band's previous releases as well as Mastodon's peers' efforts.