1. Heat: The sandstone is subjected to intense heat, usually from burial deep within the Earth's crust. This heat causes the quartz grains within the sandstone to recrystallize and interlock.
2. Pressure: Along with the heat, the sandstone also experiences immense pressure. This pressure helps to compact the grains together, squeezing out any remaining pore spaces and further aiding the recrystallization process.
These two factors combined essentially "fuse" the quartz grains together, forming a hard, durable rock known as quartzite.
