What causes the purest blue colors of turquoise?

The purest blue colors of turquoise are primarily attributed to the Persian variety, often referred to as Persian turquoise. This variety is renowned for its striking, vivid blue shades, which are the result of a specific composition and unique mineral content. The presence of copper in the mineral's structure leads to those pronounced blue hues, particularly when the stone is of high quality and has minimal alteration from other elements.

Persian turquoise has been historically prized and is noted for its consistent color and quality, making it a benchmark for assessing turquoise from various other sources. While turquoise from other regions may also display beautiful colors, the intensity and vibrancy found in high-grade Persian turquoise set it apart in terms of desirability and value. This makes it the clear choice for representing the purest blue tones in the context of turquoise gemstones.