Willie Lombard

On the shores of Lake Superior in the USA a fluorescent rock made headlines (on YouTube, anyway!). They call the normally drab rock a Yooper, after the locals from Upper Michigan. A geologist from the local university found that the sodalite in the rock causes the yellow fluorescence. I wish my sodalite would fluoresce like that! Those that do, produce only a very weak yellowish glow.

On my way to the Groot Marico Gemboree in 2018 I decided to sleep over in the Pilansberg National Park. I know the Pilanesberg crater is a source of alkaline igneous rocks like syenites and the coarser grained foyaites. On the road from Rustenberg and just before I entered the little valley before the park, I passed through a little settlement, called Ledig.

I think it is the Afrikaans word “ledig” meaning: to do nothing! What interested me, though, were the low mountains at the end of Ledig and just before the entrance to the park. Part of my hobby is the collecting of different types of rocks in South Africa and Namibia. I stopped and chiselled a few pieces from the bigger rocks to get some fresh exposures. The rocks were very coarse grained and consisted of three or four different types of large crystals. I realized I was looking at my first foyaite! The rock was looking very drab: 


That evening I washed my collected specimens and left them on the grass to dry. Later that night I used my UV-light to inspect my new collection. I was stunned! Every one of those rocks fluoresces like this below:



In the park I visited all the geosites and the only rock that was very similar to mine was the Ledig Foyaite! What else can you name a foyaite that is abundant in the town of Ledig?

I’m still waiting for my friend at the geology department of the NMMU to identify the source of the fluorescence.  Foyaites contain feldspathoids like nepheline, which is clearly visible, and sodalite, but I can’t see my foyaites glow because of sodalite! I will let you know as soon as I get my answer! WL