Last week I went to the Time in the Stone exhibition near Euston station (London) so see some amazing "stone art". My friend Sid Dawe is one of the artists who help Emily carve these big and beautiful stones. I know very little about stone but these aren't the regular kind of rocks, they're (to a layman) some sort of marble.
The exhibition is open for several more weeks and is very accessible since half the art is exhibited outside in the courtyard outside a church and the remaining other half is under the church.
This leaflet gives you all the info you need.