quartzite, a metamorphic rock that was originally a quartz-rich sandstone (see geology). It is usually pale-coloured to white, with a ‘sugary’ appearance. It should not be confused with the mineral quartz since it is a rock composed of myriad constituent grains. Once used for any tough quartz-rich rock, in modern usage quartzite refers to a compact, metamorphic fusion of the quartz grains and silica cement of the original sandstone, which makes it robust and resistant to soil erosion.
Quartzite therefore tends to form relatively higher ground with thin, poorly fertile soils, generally not well suited to viticulture, although it does occur in Germany’s nahe and rheinhessen regions, in Spain’s calatayud, and in the barossa and clare valleys, South Australia. Quartzite is much more commonly seen in vineyards as rock fragments in the soil, including the archetypal galets of châteauneuf-du-pape.