The tension between Mick Jagger and Keith Richards has threatened to tear the Rolling Stones asunder a few times, but it's also driven the band to produce much of their best music — and Richards says he and his longtime partner are still throwing sparks after all these years.

"I think the relationship is actually still in flux, or still growing — it isn't fixed. Sometimes he can get up my end, and I have no doubt that I can certainly piss him off sometimes," Richards tells NPR. "At the same time, there's a chemistry between us that we both recognize and that we know works. In a way, we're both trying to come to terms with each other. Most guys, you know where you stand with. Mick and I don't quite know how we stand with each other, and we never have."

Richards is currently enjoying some time in the solo spotlight, with his new album Crosseyed Heart out today, as well as his Under the Influence documentary. But he's already urging his bandmates back into the studio to work on a new album — and whenever they reunite, it sounds like that old friendly antagonism between the Glimmer Twins will still be there.

"Mick and I joust with each other all the time," Richards chuckled earlier this year. "From my end it’s never been a fight. Mick’s a control freak – it’s necessary for him to believe he’s ‘numero uno.’ Most of the time I go along with it, unless I think he’s making a really wrong decision affecting the Stones. … I wake up in the middle of the night sometimes and jot down a line: ‘I’ll save that one for him.’"

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