Gruta do Centenário, is a cave located in the municipality of Mariana, in the state of Minas Gerais, Brazil. It is the largest and deepest quartzite cave in the world, and second in the country in terms of unevenness. Other caves which are part of the same system have now been partially explored.
Quartzite is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of hematite. Other colors, such as yellow, green, blue and orange, are due to other minerals.
Gruta do Centenário is the deepest cave of Brazil and of the whole southern hemisphere. It is located close to the summit of the 2,070 m high Pico Alto do Inficcionado. But the most special thing with this cave is its geology: it is the deepest quartzite karst cave of the world! Quartzite is not really soluble by water, so quartzite caves are very rare, and such a big example is really extraordinary.
This cave is not accessible to tourists. Beneath its remote location, which includes a 6 hours hike from the Santuário do Caraça up the Pico Alto do Inficcionado this cave is a vertical cave and only suitable for experienced cavers.
According to Wikipedia