Cathodoluminescence microcharacterization of ballen silica in impactites

摘要

The ballen silica shows fairly weak (faint) CL with homogeneous feature in its grain exhibiting almost same spectral pattern with two broad band peaks at around 390 and 650 nm, which might be assigned to self-trapped excitons (STE) or an intrinsic and nonbridging oxygen hole centers (NBOHC), respectively, recognized in amorphous and crystalline silica. In addition, ballen silica from Lappajarvi crater shows bright and heterogeneous CL with a broad band centered at around 410 nm, presumably attributed to [A1O_4/M~+]° centers or self-trapped excitons (STE). Micro-Raman and micro-XRD analyses show that fairly homogeneous CL part is a-quartz and heterogeneous CL part is composed of a-cristobalite and a-quartz. These indicate that ballen silica could be formed in the quenching process from relatively high temperature.