Feathery and network-like filamentous textures as indicators for the re-crystallization of quartz from a metastable silica precursor at the Rusey Fault Zone, Cornwall, UK

Abstract

Hydrothermal quartz crystals, which occur in the Rusey Fault Zone (Cornwall, UK), show feathery textures and network-like filamentous textures. Optical hotcathodoluminescence (CL) analysis and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) investigations on quartz samples revealed that positions exhibiting feathery textures (violet luminescence) contain higher amounts of Al and Li than quartz positions without feathery textures (blue luminescence), while concentrations of Al and Li are significantly lower in feathery textures. Both Al and Li correlate negatively with Si. Raman spectroscopy investigations revealed the presence of a weak peak at 507-509 cm-1 in quartz affected by feathery textures, which we attribute to the presence of ≤5% moganite, a microcrystalline silica polymorph, intergrown with chalcedony. The combined occurrence of feathery textures and network-like filamentous textures in quartz samples from the Rusey Fault Zone points to the presence of a metastable silica precursor (i.e., amorphous silica or silica gel) before or during the crystallization.