Hard to tell from the photo, but it looks a bit like the damage that comes cold water splash...?

don't think so ......... colder than #º?

What do you mean by a cold water splash, sophie? Would you mind explaining?

fritz, I can't tell anything from that one particular picture.

I mean like oxidation. If basil leaves get wet with cold water and the water ends up sitting there for a while - especially through night-time temperatures - black spots can appear where the wall ruptures and the oil oxidizes. That's what it looks like to me, but yeah difficult to tell from that one pic.