Rock crystal from a locality in India’s Deccan Traps has an intense iridescence, but only on specific crystal faces. Iridescence also appears in certain forms of quartz. A thin film of iron-oxide minerals creates a bright iridescence on the face of this andradite crystal.
Less common is “rainbow moonstone” with its array of pale cyan, green, and gold structural colors. These inclusions and planes can sometimes cause thin-film or diffraction-grating interference that creates a delicate blue iridescence.
This non-iridescent effect, called adularescence, is due to microscopic inclusions or lamellar twinning planes that diffuse light. Moonstone is named for its soft, moon-like, silvery-to-bluish-white sheen. When these particles act as diffraction gratings, the stones exhibit a greenish iridescence. This non-iridescent glitter, known as aventurescence, is caused by light reflecting from included microparticles of hematite and goethite. In sunstone, a bright, golden glitter enlivens the stone’s brownish-red body color. Two other gemstones that occasionally exhibit iridescence are sunstone and moonstone, both of which are translucent varieties of feldspar minerals. Depending upon their arrangement, these layers act as thin films and diffraction gratings to create the distinctive “patchwork” of structural colors known as opalescence. It also consists of packed layers of nanoscale silica spheres. Opal is prized for its kaleidoscopic displays of fiery iridescence.
The gemstone that is synonymous with eye-catching iridescence is opal, the national gemstone of Australia. Iridescent Opal Pin this post to save this information for later. Iridescence is one of the mineral kingdom’s most beautiful displays of color. With vivid colors and infinite variations, the beauty of iridescence is indeed in the eye of the beholder. Iridescent rocks are familiar members of the mineral world that we prize such as opal and moonstone. In this bornite specimen, the primary structural colors are gold and magenta.
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