Hi elliebrown, welcome! Solid opal for a ring can be a little on the soft side and this can mean it will scratch easier. The boulder opal, because it has ironstone mixed through it, can be a better option for a ring. Another option would be to get a triplet opal which for black opal, has a black back, a thin layer of opal, topped off with a quartz cap, which should magnify the colour and protect the opal. A triplet should be considerably cheaper than a solid opal as you don't get as much opal! This quartz cap, can also be found on some doublets (a layer of opal and a top of quartz) but they usually have the black back and opal top. Hope this helps, but remember, a nice stone is still a nice stone, doesn't matter if it's boulder or black opal.
