Butt plant blooms!

My sister calls Lithops "butt plants" because they have a little crack down the center. They are succulents and exist amongst my favorite indoor flora; native to South Africa, if I remember correctly. We don't have the tag for this one any more, so I don't know the exact name, and this is the first time it has bloomed (others have gone before it). Intensely interesting plants with beautiful flowers: what more could a girl want?

Lithop [unknown species]