Daddy, I want a volcano that erupts diamonds!
The Russians apparently have one: Tolbachik in Kamchatka*. Its 2012-13 eruption included tiny diamonds called kimberlites. Normally those come from deep beneath the surface, but Tolbachik made them a different way. Instead of needing tons of pressure, these formed by the rapid cooling of gases.
Yeah, yeah. The point is: diamonds erupting from a volcano. How cool is that?