Split planchets usually occur after the strike and the coin will weigh less with a grainy appearance; the splitting can be partial, with a “hinge”, and is referred to as a clam shell. Almost all split planchets occur with planchet alloys that are mostly made of one metal like copper, silver or nickel.
Value depends on the denomination with common denomination dates worth around $40 to $70 range if dramatic enough and can climb as high as $800 if it’s a Morgan Silver Dollar. Furthermore there’s a three cent nickel that split and broke that sold for over $2,800.
Image courtesy of Heritage Auctions