Chemistry Physical Properties of Diamond Log in to track progress It has high sparkling brilliance when cut. It is a poor conductor of electricity since there are no mobile electrons. It is very hard and the hardest known substance. It has a density of 3.5 g/cm3 It is octahedral in shape. ← Previous Allotropes of Carbon Next → Uses of Diamond Leave a comment Cancel replyYou must be logged in to post a comment.