SEM backscatter image of tektite core. Dark areas are CaO poor, the light streaks are Ca and P (phosphorus) rich. The lighest streak contains up to 5% P2O5, and a grain of CaP04. [hres image]

Same Core, enhanced contrast

Polished slab of the K/T boundary ejecta layer with numerous tektite cores that still contain glass (detail above). The layer is graded, rather because of gravity flow depositional mechanism of the layer and probably not through differential settling through the atmosphere and watercolumn. The slab shown is from the B-locality (see map). With the localities discovered earlier by Maurasse, this is the only one of many that has yieldede glass remains, usually in the core of the tektites

More about tektites here