Final answer:
Sandstone commonly serves as a protolith in the formation of quartzite, undergoing metamorphism to create a hard, crystalline rock that does not react with acid.
Step-by-step explanation:
The protolith in the formation of quartzite is typically sandstone. Sandstone is the second-most common sedimentary rock on Earth, mainly composed of quartz grains. Through the process of metamorphism, where sandstone is subjected to heat and pressure, it recrystallizes into the hard, crystalline rock known as quartzite.
Varieties of sandstones such as arkose and graywacke also serve as a protolith for quartzite formation. These sandstones, under the right conditions, transform into quartzite while maintaining the original texture of sand grains. However, the quartzite that is formed is so hard that it doesn't bubble in acid, differentiating it from rocks like marble which do react with dilute acid. Renowned geologist Virginia Sisson highlights this characteristic as part of the identification process for quartzite among other rocks.