Recently bought some potted plants for my apartment and at least two of them have a few small raised black marks on, they're almost volcano shaped, but do come off with some scratching. I'm mainly just curious as to what they are. I've not been able to find anything quite like it on Google, although perhaps I'm searching for the wrong thing. The closest appears to be black sooty mold, but these are far more sparse and regular. Picture attached in which you can see two of these marks on a leaf. Any ideas what they could be?
What you have are scale - sap-sucking insects that protect themselves with a dome-shaped shell.
I suggest that you get rid of them asap, if they multiply, your plants will likely suffer.
See other Q/As tagged scale for treatment options. If you have just a few, wiping them off may suffice, but you need to keep a close eye on the plants for a while to make sure you also remove whatever young ones may still hatch. (They will be a lot smaller!) Note that while the ones in your photo are in the middle of the leaf, typical hiding spots are the underside of the leaves and the joints of leaves and branches.