During this era, hard stone vessels made of slate, metamorphic schist, diorite, and basalt first appeared. All but indestructible, these items are among the most unusual and enigmatic of the ancient world. I have no idea. . . . The Egyptian of that time had at his disposal only stone, copper, and abrasive sand. . . . It is more difficult to imagine the fabrication of hard stone vases with long narrow necks and rounded bellies.
Metamorphic schist is harder than iron.
The diorite used, a granitic rock, is among the hardest known. Modern sculptors do not attempt to carve these varieties of stone. Yet, these vessels were made before the introduction into Egypt of metals strong enough to cut hard stone. Numerous vessels have long, narrow necks and wide, rounded bellies. Their interiors and exteriors correspond perfectly.