Colour changing in light-sensitive minerals exposed to UVA 340 nm rays

Abstract

Some minerals suffer from colour variations when exposed to incident sunlight. The minerals which possess this property are defined as “photosensitive”, and their colour changes especially under UV radiation. This work targeted this phenomenon and selected 27 among the most widespread and widely occurring mineral phases for. Initially, the chosen minerals have been characterised chemically (SEM-EDS) to detect common impurities often responsible for the chromatic alteration; subsequently, these minerals were exposed to UVA 340 nm rays at 0.35 W/m2. The chromatic shifts were measured in the CIELAB space immediately after the artificial ageing to identify the changes with respect to the initial colour. The results show that only 11% of the minerals displayed slight chromatic changes, i.e. imperceptible to the naked eye, while 89% of the chosen minerals manifested visible color change with relative perceptual difference ΔE ranging from 3 to 32.