Crystal opal is the most well-known type of opal among most people. It has a transparent body, and the play of colors is displayed based on the transparent body. The play of colors in crystal opal can be classified into red fire and blue-green fire. Generally, crystal opals that exhibit visible red fire are categorized as red fire opals, while those displaying blue-green fire are classified as blue-green fire opals.
Although we simply summarize its colors in a few words, the play of colors in opals goes far beyond what words can describe. A high-quality red fire opal not only showcases red fire but also exhibits blue fire, green fire, golden fire, and even purple fire. This is determined by its chemical structure. Blue-green fire crystal opals, on the other hand, mostly display blue fire and green fire. It takes longer and more stable geological conditions to form a high-quality red fire opal compared to blue-green fire opals. As a result, red fire opals are less abundant and more valuable, which is particularly evident in black opals.
Not every crystal opal has an absolutely transparent body. There are also relatively opaque or semi-transparent ones. A high-quality crystal opal is characterized by both high transparency of the body and strong play of colors. On the other hand, if a crystal opal has intense play of colors but a slightly opaque body, its price is lower than the former.
Due to the significant variation in the body and play of colors of crystal opals, their prices can vary greatly. They range from affordable prices in the hundreds of dollars to collector's items with high prices.
The term "crystal" in crystal opal can often lead to the misconception that it is a type of quartz crystal. However, this idea is incorrect. "Crystal" simply refers to its clarity and transparency. In fact, opal is a hydrated amorphous form of silica, not a crystalline material. It does not have the symmetry or irregular geometric shape typically associated with crystals. The formation of opal is highly dependent on the specific geological conditions at the time and is often mixed with other minerals. Therefore, cutting and polishing opals is a challenging task.
