Step 4: Gem Grading

Lesson 18

Opal Grading and Terminology

Our IGS opal price guide uses a grading system unique to opals. You can find a full explanation of this system and its terminology in our article on appraising opals. Here’s a brief review:

  • Opals have grades of below commercial, commercial, good, fine, and extra fine. These assessments cover an opal’s colors, directionality of flashes, imperfections, and cut.
  • Body tones, from N1 (black) to N9 (white), describe the base color of a stone, without play of color. Gemologists use this system to distinguish black, dark, light, and white opals. Stones from N1 to N4 are considered black opals. N5 to N6 are considered dark opals. N7 to N8 are considered light opals. An N9 is considered a white opal.

Opal Buying and the Four Cs

Opals can still be evaluated in terms of color, clarity, cut, and carat. However, to properly judge their value, you have to consider some factors unique to these gemstones.


Color is the most import factor for evaluating an opal’s value. You must consider the number of colors present, the clarity of colors, the brightness of fire, and the play-of-color…