Sapphire is a gem quality variety of the mineral corundum. It is the second hardest substance on earth after diamond.While blue is the most traditional and classic color for sapphire, sapphire is actually found in a variety of different colors. Most natural sapphire is quite pale and light in color. Only a small percentage of natural sapphire exhibits vivid and intense colors without some type of treatment or enhancement, the most common being heat-treatment. Sapphire lacks cleavage, but can exhibit a conchoidal, uneven fracture. Sapphire colors are best viewed under natural daylight. In artificial or incandescent light, sapphire colors can appear darker and inky black-blue. Many may even appear redder and less attractive than they really are. Sapphire colors are a result of trace impurities. Sapphire can occur transparent to opaque. Transparent materials are the most valuable.