Talk about a weapon of mass value -- Darth Vader’s iconic lightsaber is about to hit the auction block ... and this bad boy’s expected to rake in Jedi-mind-blowing cash.

TMZ got Brandon Alinger , COO of Prop Store, on cam -- and he makes it clear, this isn't some random hunk of plastic ... it’s the screen-matched Hero Dueling Lightsaber used by Vader in "The Empire Strikes Back" and "Return of the Jedi."

Catch the full clip ... 'cause Brandon gives us his prediction of what he thinks it'll fetch, and the number is high, especially since the absentee bid is already over a million bucks! Play video content

For context, Brandon says their biggest "Star Wars" score to date was an X-Wing Fighter model that sold for $2.3M -- so, yeah, the Force (and the $$$) is strong with this one

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