Subject: What is Diarite? I can't kind find it listed in any Geological Refs

A program about the pyramids in Egypt mentioned this mineral as the one that some sarcophagi inside the pyramids, were made of. The program said this rock(?) / mineral(?) was the hardest on earth. It was mentioned because, it is not known how the Egyptians drilled them out so perfectly square with the technology available to them at the time. Phoneticly it was DI-ER-RITE. I was interested in more information about this substance i.e. it's properties and where it's found etc.. Thank you.

Re: What is Diarite? I can't kind find it listed in any Geological Refs