Causes of iridescence in natural quartz

Xiayang Lin, Peter J. Heaney

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2 Scopus citations


Iris quartz specimens from geodes in the Deccan Trap basalts of west-central India have been described since 1860. These quartz crystals exhibit dominant terminal faces, and iridescence is visible on only the minor z {011} faces and not the major r {101} faces. For this study, we analyzed iris quartz crystals from India's Jalgaon District using scanning and transmission electron microscopy (SEM and TEM) and atomic force microscopy (AFM). SEM and AFM imaging revealed that the iridescent z faces exhibit periodic ridges with wavelengths from 400 to 700 nm, but no surface topography was apparent on the non-iridescent r faces. TEM examination of a section removed from a z face by focused ion beam (FIB) milling suggests that the ridge and valley structures were produced by preferential etching of periodic defects on the z faces, creating a diffraction grating. We interpret these defects as paired Brazil twin boundaries.

Original languageEnglish (US)
Pages (from-to)68-81
Number of pages14
JournalGems and Gemology
Issue number1
StatePublished - Mar 1 2017

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology


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