When sandstone is heated and pressed, it transforms into a metamorphic rock called quartzite.

Here's how it happens:

* Heat: The intense heat causes the quartz grains in the sandstone to recrystallize, forming larger, interlocking crystals.

* Pressure: The pressure from the surrounding rock layers squeezes out any remaining pore spaces and cements the quartz crystals together.

The result is quartzite, a very hard and durable rock that is often used for building materials and countertops. It has a distinctive, glassy appearance and can be found in various colors depending on the impurities present in the original sandstone.