sentences:  Prior to this work, evidence for man's first use of diamond was known primarily from Indian texts dating to the latter half of the first millennium BC, and there was no reported evidence for its use in prehistoric times.In 2005, Lu and collaborators reported strong evidence that the ancient Chinese used diamonds to polish ceremonial stone burial axes as early as 2500 BC, placing the earliest known use of diamond two thousand years before the mineral is known to have been used elsewhere.These stone axes, made predominantly of the mineral corundum (sapphire and ruby in its colorful gem forms) were fashioned as early as 4000 BC, so that they represent the earliest use of the mineral corundum, as well.