Iris Quartz aka Rainbow / Iridescent
In 1950 Dr. C.V. Raman (father of Raman Spectroscopy) published the discovery of a colorless Quartz that exhibits adularescence, or iridescence. It occurs in druse veins emplaced in basalts, and it has also been discovered in Argentina on the slopes of a volcano. Jack has found a good source for very fine specimens from India, and we now offer them on this website.
We call it Iris Quartz, but it's also sold as Rainbow Quartz, Iridescent Quartz and "Anandalite" (a marketing term).
It is difficult to capture all the colors that a specimen displays in a photo. Rest assured that these specimens will show neon color in nearly all the crystals on a specimen, changing as the specimen is viewed from different angles. The colors are due to polysynthetic twinning in the crystal; and this is not the same as interference pattern rainbows seen in fractures of clear quartz. The cause of this structure in basalt related quartz has not been determined.
Amethyst discovered by Jack Lowell in Uruguayan Basalts exhibits this optical phenomenon and is named Lowell Effect Amethyst by the Gemological Institute of America.