I don’t get it, doc, if it was stone how was it used to draw a picture?
They powdered the fossilized rock and mixed it with an ammonia solution:
"They cracked open what appeared to be an ordinary looking rock only to find the one-inch-long black ink sac inside.
After realising what they had stumbled across, they took out a small sample of the black substance and ground it up with an ammonia solution.
Remarkably, the ink they created was good enough to allow them to draw the squid-like animal and write its Latin name."