Spectral Colours Of Iris Agate Revealed: What Causes Them In Transmitted Light?
Channel: gemmology
Date: 2020-05-30

Exploring the Science Behind Iris Agate: The Stone That Produces Spectacular Color When Viewed In Transmitted Light

Iris agate is agate whose thin section shows spectral colours when viewed in transmitted light. These colours are not thin-film colours such as those of precious opal.
 In 1935 when Fred S. Young and Dr. H. C. Dake first showed the author thin slices of iris or rainbow agate, the display of colours recalled the similar appearance of a diffraction grating. Microscopical examination soon confirmed the opinion that a periodic banded structure existed in the agate, and revealed interesting correlations with the chalcedony's structure and variations in fineness and regularity.
OCCURRENCE: South Africa, USA, Indonesia
Sources: American Mineralogist, Volume 37, pages 578-587, 1952 by FRANCIS T. JONES, 244 Trinity Ave., Berkeley 8, California.