It looks nothing like marble, but at this point I couldn't care less.
I don't even care that this picture is crooked.
Now all that's left is to buy baseboard material and get that installed, and then buy something out of which I will create thresholds at each doorway.
I looked at marble thresholds today but they are too think and would be a tripping hazard. I'm thinking something very, very thin. I might go with pieces of laminate flooring in which case I'd have to cut off the tongue/groove nonsense and then paper and poly them to match the floor. Maybe I can find similar material that doesn't have the tongue and groove nonsense.
In any case, as I said: Huzzah!