Written Characters in Black Opal

Makoto Miura

Opal sometimes contains play-of-color patches with unique and attractive patterns, such as an impressive 8.13 ct black opal measuring 15.93 × 10.88 × 7.52 mm recently examined by the author. Based on its gemological properties, microscopic observations, and strong phosphorescence to long-wave ultraviolet light, the stone was natural opal with no signs of assembled features.

Interestingly, blade-like play-of-color patches with a striking brushstroke pattern were present within the common (nonphenomenal) opal area on the back side (figure 1). Some of the patches intersected at nearly 90° and resembled Chinese characters. This pattern is rarely seen in precious opal and is known as a “Chinese writing pattern” in the trade. On the other side of the stone, the play-of-color formed another unique pattern, this one resembling the Latin letter “A” (figure 2). Brightfield illumination revealed that these blade-like play-of-color patches were also contained within the common opal area (figure 2, right). The combination of reflected light with fiber-optic illumination and brightfield illumination caused the patterns to look like a natural inscription within precious opal. It is interesting to consider how play-of-color patches and common opal were both created from hydrothermal fluids.