The changes or the transformation of an existing rock because of chemical changes, pressure and temperature is known as metamorphism. During the process of metamorphismm the existing rock change its texture geologically but they do not turn into a liquid magma.
When sandstone is subjected to heat, pressure and any other natural agencies Quartzite is being formed. Quartzite is a metamorphic rock and it derived it hardness mainly from its richness in quartz.
