While the value of metals such as gold, platinum and silver fluctuate and go in and out of fashion as consumer taste demands, the desirability of gemstones appears to be constant, with almost any item of jewelry bearing a genuine gemstone seen as alluring and valuable, but what are the most precious gemstones? Precious tastes Rich blue in color, tanzanite is very highly prized. Part of the reason for its popularity and high cost – around $600-1,000 per carat – is because it is only found in one place in the world, and that is in the foothills of Mount…