Turquoise Grading Guide
How the Standard Reads a Stone
The question is not whether a stone is beautiful. The question is how rare the visible natural formation is when compared to authorized Master Stones.
Look First, Then Grade
The Standard is built for direct visual comparison. A grader evaluates the finished face of a natural turquoise cabochon against the authorized Master Stones for Color, Matrix, and Zat, then records the official result according to the 2026 edition.
The Three Grading Attributes
Color
Color refers to hue, tone, and saturation. Color Master Stones represent rarity rather than preference across the Blue, Blue-Green, Green-Blue, and Green color families.
Matrix
Matrix refers to the presence of host rock or associated minerals in which turquoise is formed or embedded, in the finished stone.
Zat
Zat is the visual impact of the stone: how vibrancy, brightness, contrast, and overall pop work together to engage the eye.
Common Questions
Can a lower grade stone still be valuable?
Yes. The Standard grades rarity of natural formation. Market value can also depend on provenance, size, demand, artistry, condition, and buyer preference.
Can a high grade stone have unknown provenance?
Yes. Official Grade is assigned independent of provenance. It records the observed grade under the current edition.
Does the grade prove provenance?
No. Provenance means the source or origin of a turquoise specimen. The Standard does not certify provenance, chain of custody, or collector history.
Is spiderweb always better?
No. Matrix grade is based on rarity within the matrix methodology. A pattern may be attractive without matching a higher Matrix Master Stone level.
Can green turquoise grade high?
Yes. Color Master Stones represent rarity rather than preference. Green, Green-Blue, Blue-Green, and Blue are evaluated within their defined color families.
Who decides the grade?
Official grades are determined only through the procedures established by the current publication using authorized Master Stones and the prescribed grading methodology.