Whilst most rocks on the planet are made up of several different minerals some are made up of just one. Quartzite which is composed almost entirely of quartz formed through the metamorphism of sandstone. Sandstone is a common sedimentary rock that contains minute grains of quartz.
In its purest form quartzite is usually white or grey although the presence of iron can cause various shades of pink or red. Inclusions of chromium rich mica changes the colour of quartzite to green. This green coloured stone is better known as green aventurine. Different colours present in quartzite will be caused by inclusions of different minerals.
Quartzite is an extremely hard stone that's resistant to chemical weathering. It can sometimes resemble marble which formed through the metamorphism of limestone. Marble is softer than quartzite.
The reason quartzite is so tough and durable is because its made up of a network of tightly interlocking grains of quartz.