What percentage of water does most opal contain?

Most opal contains a significant amount of water, which contributes to its unique optical properties and play-of-color. The correct answer indicates that opal typically contains between 3 to 10 percent water. This water content is essential to the formation of opal, as it fills the voids in the silica structure, leading to the formation of the stone's distinctive characteristics. The presence of this water also affects the stone's physical properties, including its stability and how it responds to changes in temperature and humidity. Such knowledge is crucial for gemologists, as understanding how water content influences opal's behavior can inform decisions about care, grading, and value.