A question resolved

In December 2000 I published a note in Australian Geomechanics with several scanning electron microscope photographs (SEM) of Hawkesbury Sandstone I had taken in 1978. Figure 1 is one of the photographs. I asked the question, “What is the strange tentacle-like material etched into the quartz grains and apparently acting as a cementing agent?” All I, as an engineer, knew at the time was that electron probe work showed this material to be a potassium aluminium silicate. At that time nobody offered a satisfactory explanation.