I never said it was sapphire, just that the owner was told it was somehow related and an unknown proprietary military material. I have no idea what it was, only the empirical properties and what happened with it. Disputing the empirical is insane. Speculating about what it could have been is the only space to talk about.
The job and requirements were specified in advance. Whomever setup that job presumably did the engineering to know what could be done. It took a bunch of inserts to machine it. It was entertaining to watch. But I was just operating a manual Bridgeport mill and helping when asked.