Diamonds occur in nearly all colors, the three shades most in demand being blue white, steel white, and pure white. The steel white has no perceptible color, but their lustre resembles that of polished steel. They are rare Indian stones and always obtain fancy prices.. A blue white stone has only the faintest tinge of blue. The most complete collection of colored diamonds in the world is in the Vienna Museum. Their order in regard to rarity and value is as follows: blue, red, green, White, olive, black, fire colored, yellow. The blue diamond when perfect in color, which must be darker and unlike the soft vel vety shade of the sapphire, is the rarest of precious stones, and has only been found in the mines of India. A coal black diamond weigh ing 350 carats, was exhibited at the World's Fair in London, in 18 51, as a great curiosity. It was so hard that it resisted every effort made to polish it.