This section is from the book "Bepler's Handy Manual of Knowledge And Useful Infomation", by David Bepler. Also available from Amazon: Bepler's Handy Manual of Knowledge and Useful Information.
Diamonds averaging one-half carat each, $60 per carat; diamonds averaging three-quarters carat each, $80 per carat; diamonds averaging one carat each, $100 per carat; diamonds averaging one and one-quarter carats each, $110 per carat; diamonds averaging one and one-half carats each, $120 per carat; diamonds averaging one and three-quarters carats each, $145 per carat; diamonds averaging two carats each, $175 per carat. In other words the value of the gem increases in the geometrical ratio of its weight. Four diamonds weighing together two carats are worth $120; but one diamond weigh-ing just as much is worth $350. Stones weighing over two carats are about the same price per carat as two-carat stones; they should be dearer, but they are not simply because the demand for them is limited. If the demand for diamonds were as imperative as the demand for flour or beef the geometrical ratio would again come into play, and five-carat stones would be valued in the thousands.
The largest diamond-cutting house in Amsterdam, Holland, is the Amsterdam where they employ 400 men. The famous Kohinoor diamond was cut there. The cutters make from $7 to $12 and even $14 per day.