Physical Properties of Diamond by keypoint 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. Others are Viewing: Physical Properties of Graphite Physical Properties of CO2 Physical Properties of CO Physical Properties of Acid Physical Properties of Bases Uses of Diamond Chemical Properties of CO2