"Petra, founded by serial entrepreneur Kim Abrams, says it's demonstrated the robot's capabilities by boring a 24-inch tunnel through 20 feet of Sioux Quartzite – which Abrams describes in a CNBC interview as "the hardest rock on earth ... harder than bluestone granite ... the type of rock that would normally have to be dynamited." Swifty progressed at a rate of an inch a minute."
https://newatlas.com/technology/petra-thermal-drill-robot/
https://newatlas.com/technology/petra-thermal-drill-robot/