What would cause/allow a planet with very high gravity to have tall, sharp mountains?
Mountain height is generally capped off by gravity, erosion, and the mountains composition. On a higher gravity world, mountains likely wouldn't be able to get very tall or jagged, but I love the idea of a planet having harsh, steep terrain AND gravity high enough to make travel even more hellish for nonnative explorers.
Ideally, I'd have the gravity be 1.5-3 times that of earth.
For visual appeal, I'd also prefer the rocks making up the mountains and crust to be primarily black or dark grey in color.