Mount Everest has been believed to be Non-Volcanic and is perhaps the Tallest mountain in the world, having been formed primarily by Tectonic Forces.

Had Everest been born as a Volcano, not only could it be the Tallest, but there is the chance it could also produce Violent eruptions (VEI 5-7) that would, thus, give it a completely different appearance compared to what it is seen as in Reality.