Publications Details
Evidence of depletion of iron from natural quartzite during laser-driven hydrothermal processing
A sample of natural quartzite rock was submerged in deionized water and illuminated with 1.8-J pulses of 527- nm light with 15-ns duration over an area of 3 cm2 [fluence = 0.6 J/cm2]. This relatively low fluence and intensity [40 MW/cm2] were far below the threshold needed for direct ablation via plasma formation or thermal evaporation. With each laser pulse, a small cloud of sub-μm particles was released from the surface and dispersed into the submerging water, forming a long-lived suspension. After one hundred laser pulses, the processing was terminated and the surface of the originally colored quartzite was rendered colorless. The quartzite rock was cut in cross section and the colorless material on the surface was examined with X-ray fluorescence. We report that the transition element Fe was found to be significantly depleted in this colorless layer. This supports the hypothesis that the laser exposure lead to a transient hydrothermal dissolution of the material, followed by a recrystallization process of the SiO2 that preferentially released iron oxides into the submerging water.