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Is the special node in the space marines head that carries the gene seed, the one the apothecaries go after, durable. Like if a marine takes a starcannon shot the chest, it vaporizes his body, would the gene seed survive like the black box on an airplane, or would it get vaporized too?
Space Marines are the gateway drug
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Geneseed is still only an organ, normally die to marines natural toughness and power armour the geneseed survives but if hit by a starcannon (a nice peice of hot toasty plasma) it would probably vaporise it.
A marines would have to be hit with something heavy to be vaporised (more along the lines of instant death) and plasma usually does the trick.