Turquoise

Turquoise from Iran is often said to be the best and sometimes it has a clear sky blue color, with no green overtone and no black or brown veins running through it.

Turquoise is more expensive when it has an intense blue color without green overtones.

Because of its porous nature, the color of turquoise can be improved by impregnation and heating with dyes and other materials.
Most turquoise on the market today has been treated by one or more of these methods.