Cathodoluminescence Spectral Characteristics of Quartz and Feldspars in Unaltered and Hydrothermally Altered Volcanic Rocks (Almeria, Spain)

The volcanic rocks of the Cabo de Gata region have been transformed by hydrothermal alteration, forming in some areas, highly silicified and feldspatized rocks. Various samples from outcrops of unaltered and hydrothermally altered volcanic rocks were studied by conventional transmitted-light microscopy to determine their genesis (magmatic, inherited or neoformed) and scanning electron microscope cathodoluminescence to define their spectral features. The magmatic quartz shows emission bands at 400, 440, and 480nm., and these bands disappear or decrease in the secondary hydrothermal quartz, characterized also by an intense emission band at around 570–580 nm, and another around 460 nm. The inherited magmatic plagioclase and neoformed anorthoclase have some similar emission bands and their genesis is not marked by cathodoluminescence features. The magmatic K-feldspars (sanidine), have emission bands at around 425, 440, and 490 nm, constituting a strong blue emission (420–500 nm). This emission is wea...