Physical Properties of Diamond

HARDNESS:
Diamond is a perfect "10", defining the top of the hardness scale, and by absolute measures four times harder than sapphire (which is #9 on that scale).

CLARITY:
Diamond is transparent over a larger range of wavelengths (from the ultraviolet into the far infrared) than is any other solid or liquid substance - nothing else even comes close.

THERMAL CONDUCTIVITY:
Diamond conducts heat better than anything - five times better than the second best element, Silver!

MELTING POINT:
Diamond has the highest melting point (3820 degrees Kelvin)