Diamond is the hardest material known to man kind. When used on tools, diamond grinds away material on micro (Nano) level. Diamond is the hardest substance known and is given a value of 10 in the Mohs hardness scale, devised by the German mineralogist Friedrich Mohs to indicate relative hardness of substances on a rating scale from 1 to 10. Its hardness varies in every diamond with the crystallographic direction. Moreover, hardness on the same face or surface varies with the direction of the cut.

Diamond crystallizes in different forms. Eight and twelve sided crystal forms are most commonly found. Cubical, rounded, and paired crystals are also common. Crystalline diamonds always separate cleanly along planes parallel to the faces. The specific gravity for pure diamond crystals is almost always 3.52. Other properties of the diamond are frequently useful in differentiating between true diamonds and imitations: Because diamonds are excellent conductors of heat, they are cold to the touch; Most diamonds are not good electrical conductors and become charged with positive electricity when rubbed; Diamond is resistant to attack by acids or bases; Transparent diamond crystals heated in oxygen burn at about 1470° F, forming carbon dioxide.