Was having a picnick wiht some friends on the rocks on the southern tip of the southernmost island in Suomenlinna, when I spotted this. What originally attracted my attention was a some small-scale folding visible in a layer of dark minerals, but I noticed that under it there were some large-ish black crystals that didn't look like the micas that usually make up most of the mafic minerals in granite. I believe they are black tourmaline, as I have a very similar-looking tourmaline crystal that I found in a pegmatitic granite in Kemiö (that one's niicer, though; you can actually see the hexagonal shape of the crystal in that one).
The rock itself is a granitic rock (granite, or maybe granodiorite) that has undergone some degree of migmatization. It's not nearly as coarse-grained as the pegmatites in Kemiö, so I was quite suprised to see this big tourmaline crystals in it.