Step 4: Gem Grading

Lesson 18

Opal gemstones are evaluated a little differently than other gemstones. The International Gem Society opal price guide features a grading system and terms unique to opals. A full description of these differences can be found in our Premium article on Appraising Opals. For the benefit of those interested in opal buying, here is a brief explanation of these terms.

  • 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. This system is used 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 4 Cs

Opals can still be evaluated in terms of color, clarity, cut, and carat. However, you’ll find opals have some additional conditions that must be taken into account to properly judge their value.


Color is the most import factor for…