As Keith Richards tells it, the Rolling Stones' first-ever all-blues album is the result of the band learning how to play in the unfamiliar surroundings of Mark Knopfler's British Grove Studios.

To ease into the new place, the Stones decided to knock out a version of Little Walter's "Blue and Lonesome" and it sounded good enough that the band decided to cut a few more covers, winding up with a full album of Chicago blues in a few days.

The Stones haven't worked at such swift speed in decades -- not since the early '60s, when they were churning out two albums a year -- and much of the appeal of Blue & Lonesome lies in its casualness: by being tossed off, the album highlights how the Stones play together as a band, blending instinct and skill.

Blue & Lonesome isn't a showcase for virtuoso playing -- even Eric Clapton's two smoldering solos are part of the tapestry -- but rather a groove record, emphasizing feel and interplay while never losing sight of the song.

Such commitment to song is one of the reasons Blue & Lonesome winds up as an unexpected triumph from Mick Jagger.

A blues album from the Stones always seemed like a dream project for Keith Richards, who always championed the band's blues roots, but it's Jagger who dominates the album, playing searing harp and singing with nuance and power.

Always a guarded performer -- back in 1974, he scoffed at the notion of letting his feelings flood on the page -- Jagger seems freed, pouring heart into the slow burners and uptempo shuffles alike.

The rest of the Stones match his commitment and that's what makes Blue & Lonesome something remarkable.

Conceptually, it's clever -- if this winds up being the last Rolling Stones album, it provides a nice bookend to their 1964 debut -- but it's artistically satisfying because it's the Rolling Stones allowing themselves to simply lay back and play for sheer enjoyment.

It's a rare thing that will likely seem all the more valuable over the years.