Whats the difference between precious opal and fire opal?
Precious opal refers to an optical phenomenon; fire opal refers to a body color. The delightful flash of colors in a fine eem opal is properly called play-of-color, although we often react to this phenomenon by saying: “Wow, look at the fire in that one!” Regardless of what we call this rainbowlike effect, what we admire in opals (as well as in well-cut diamonds, CZs, and other stones) are the colors of the spectrum spread out before us. When we see these spectral colors in opal, we call the material precious opal. This colorful display is the result of diffraction. Structurally, precious opal is a three-dimensional array of very tiny spheres of almost equal size aligned in such a way as to separate or diffract white light into some or all of the different colors of the spectrum. You know how you see “rainbow” effects on the surface of a CD? Tiny lines on the CD act as a diffraction grating to produce that effect. You can think of precious opal as a sort of three-dimensional equivalent
