it varies from region to region, but I know that moss will grow on shales and slates, granite, some sandstones, and marble...actually, in my humid climate, even the basalt and granite will support moss- but the locals around here are more likely to want to STOP moss, rather than encourage it.

Ditto. Limestone (due to its pH) is probably the only surface I would not try, although I have actually seen moss on that too. Remember too, you don't need rocks to grow moss. Dirt can work just as well.

thanks yall. much appreciated.

I placed fossils in limestone in the woods and have had no problem getting moss on them. Granted, most have been in the woods for 20 years! Lately I have been harvesting the fossils, putting them in my back yard. I think the key is shade and plenty of organic humus like decomposing leaves.

In Texas and OK, "moss rock" is sandstone.

AlanRocks, the same here. I'm a geologist and can definitely say that most of the rocks in our garden are limestome. We can grow moss on them if they are kept damp.

I also collect fossils. Our rock gardens have as many fossiliferous rocks as non-fossiliferous. Everything from dinosaur bones, to pertrified wood to slabs of various paleozoic invertrbrates from our nearby mountains. I also insert a lot of fossils (brachiopods, ammonites, etc.) into hypertufa troughs to give them added character.