The international gemological community classifies turquoise into four grades:

• Grade 1 (Persian): Includes three types. The highest grade is a strong to medium blue, with a soft and even color, no dark or pale blue spots, no iron lines, strong luster, translucent, with a glassy surface, small porosity, and high relative density; Persian spiderweb turquoise is of superior color and texture but has an attractive spiderweb pattern on the surface; Persian iron-lined turquoise is of superior color and texture but contains varying amounts and forms of iron lines.

• Grade 2 (American): Light blue in color, less vibrant than Persian grade, with poor transparency, opaque or slightly translucent, weak luster, mottled structure, with slightly lighter or darker areas, mostly without iron lines; or with fine spiderweb patterns; or containing varying amounts and forms of iron lines.

• Grade 3 (Egyptian): Blue or blue-green in color, usually selected from Grade 1, denser than American turquoise, but the color is less appealing, with more iron lines; lower grade has limited market demand.

• Grade 4 (Afghanistan Grade): Light or dark yellowish-green in color, with more iron lines, it is an inferior product with very little market value.

Chinese Arts and Crafts Grading System

• Grade 1 Turquoise: Bright sky blue, pure and even color, strong luster, translucent to slightly transparent, with a glassy surface. Dense, fine, and tough material, no iron lines or other defects, large size.

• Grade 2 Turquoise: Deep blue, blue-green, or emerald green in color, extremely strong luster, slightly transparent. Tough material, few iron lines or other defects, medium size.

• Grade 3 Turquoise: Light blue or blue-white, light yellowish-green, etc., poor luster, stiff texture, obvious iron lines, or more problems such as white spots, veins, and hollow core, varying sizes.

Classification by Texture

• Porcelain Turquoise: The hardest turquoise, with a hardness of 5.5-6, mostly pure sky blue in color, the highest grade of turquoise.

• Turquoise: Its color ranges from bluish-green to pea-green, with a hardness of 4.5-5.5. It is a medium-quality turquoise.

• Pale Turquoise: Also known as fibrous turquoise, it ranges from pale blue to off-white, with a hardness below 4.5. It can be scratched with a knife and is considered the lowest quality turquoise.

• Spiderweb Turquoise: Turquoise contains fine black goethite veins distributed in a network. If the veins are fine, firmly bonded, and hard, they integrate with the turquoise, creating natural patterns resembling ink lines. This is beautiful and unique. Turquoise with beautiful spiderweb patterns can also be considered a high-quality piece.