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How to Grade Opals

Grading opals is sometimes challenging as they exhibit strange and beautiful colors across a broad spectrum. Opals come in vast quantities of rainbow colors, and most are mined in Australia. Grading an opal can be a subjective task due to the differing desires of consumers. Read the steps below to better narrow the decision-making process.

Instructions

- 1
  Determine the color variation according to personal taste. Opals cover a wide gamut of light play across the stone, and light and dark stones transfer light differently. The four common color categories for opals are black, boulder, crystal and white.
- 2
  Look at the cut of the stone. Most opals are flat-cut to best show the gem's fiery luster. There are opals that are rounded or cut into ovals as well.
- 3
  Find any imperfections on the opal. Opals sometimes exhibit a webbing effect across the surface, which is considered undesirable. Avoid split or cracked opals.
- 4
  Seek out the highly desired and rare opals. Very dark opals, such as fire opals, are suitable for faceting or fancy cuts. The softness of the gemstone is typically the reason for flat-cut examples. Black opals from Lightning Ridge and Mexican Fire Opals are of the rarest variety and are highly valued.
- 5
  Check the opal for specks of color called pin-fire. Also look for large flashes called flash and angular patches called harlequin.

Gemology