This is my alltime favorite cactus! (at least right now...)
This species comes from the Sucre region of Bolivia where it grows high in the mountains. The black and purpla and green colors are just awesome. Some plants have little purple, and some have yellow rather than gold spines.
You will see this plant as Rebutia rauschii and Edward Anderson, in his wonderful 2001 book The Cactus Family considers this species to really be Rebuita steinmanii or Rebutia canigueralii. I have two plants of rauschii and they do look rather different. I'm sticking to the name rauschii until I get to look at the original papers.