TURQUOISE is one of the world's most ancient and revered gemstones, prized for its unique robin’s egg blue-to-green color and its historical significance across many civilizations. Here are the detailed specifications and characteristics of turquoise, covering its science, history, and grading. While defined by its blue-to-green hue, the appearance of turquoise is highly variable, influenced heavily by its geographical origin and mineral inclusions. The "ideal" turquoise color is a pure, intense "robin’s egg blue" or "Persian blue." One of the most defining characteristics of turquoise is its matrix—the web-like or patchy network of brown, black, or grey rock that is often visible on the stone's surface. The matrix is remnant rock (like limonite, sandstone, or pyrite) from the host formation in which the turquoise grew. Common, larger inclusions that decrease the value unless the stone is exceptionally large or unique. Extremely rare and highly valuable; often called "Persian" grade, as the finest historic stones had zero matrix.