Everybody knows and loves the unique sky-blue of turquoise, but rarely is it thought of in the same light as other blue gemstones. Yet it is December's birthstone and the 11th wedding anniversary stone. Of course turquoise is most famous for its Southwest flavor and Aztec, Mexican lore. But it was also highly prized by ancient Egyptians who fashioned it into jewelry and offered it to the gods in burial ceremonies.

The highest quality and most precious blue turquoise is found in Iran, and other sources are Egypt, Turkistan and Mexico. And one might think that the stone would thrive in such arid climes. Interestingly, though, since turquoise is so porous, it will discolor from its famous blue to green or brown and dehydrate rapidly in such conditions. The top quality variety from Iran (where it is the national stone) on the other hand, tends to be more stable and its color can withstand the heat more readily.

Therefore, most all turquoise is treated with a type of plastic for durability and color maintenance. There is also a wax impregnation process for color enhancement. If you are about to purchase some expensive turquoise jewelry, find out if it has been treated and get "genuine untreated turquoise" clearly stated on your receipt if the dealer is making such claims.

Turquoise reached the pinnacle of its popularity in the 1970's when it was selling like "hoola-hoops," commanding thousands of dollars for pieces that now sell for about a tenth of those hey-day prices.