Minas Gerais is a world famous name among mineral collectors. This state produces the meat of all semi-precious minerals. Most important are the topaz (Al2SiO4(F,OH)2) and tourmaline (NaFe+++3Al6(BO3)3Si6O21F) production.
The state of Minas Gerais produces about 80% of Brazil's precious gems and minerals. Gold was first discovered near Ouro Prêto around 1700. Gems mined in the region are diamonds, emeralds and topaz. Diamantina was once the biggest diamond producer in the world, but today it is famous for rare quartz crystals.
The tourist mines in Minas Gerais are historic, interesting and exciting but don't take along your friendly mine inspector or tell your insurance company too much!
The same area is also famous for numerous caves, with most interesting geologic phenomena and extraordinary speleothems. At the moment more than 500 caves are listed in the cave register. An impressive superlative is the longest stalactite of the world at the Caverna Janelão, which is 28 m long. Gruta do Centenário is the deepest cave of Brazil and of the whole southern hemisphere with a vertical range of 481 m.
To the North of Belo Horizonte, a little south of the center of Minas Gerais, is the location of one of the most important Brazilian carbonatic karst areas. It is called Lagoa Santa Karst, developed in the limestones of the Sete Lagoas Formation (Bambuí Group), which consitst of very pure calcarenites (CaCO3>94%). The whole area is intensive karstified and shows numerous karst features like numerous coalescent dolines or sinkholes. Other common features are the big linear cliffs, the results of doline evolution, canyons, and blind-valleys. Also many poljes, large lowered plains which are seasonally flooded.
This karst area has hundreds of caves, of which numerous are paleontological sites of great value. They contain specimens of the extinct Pleistocene megafauna, and important vestiges of the pre-historic human occupation of Brazil. In Gruta Lapinha the Danish scientist Peter Wilhelm Lund described 12,000 year old human bones of the Homem da Lagoa Santa (Lagoa Santa Man). He lived in this area from 1835 to his death in 1880.
The region is today in a process of intense urban and industrial development. To protect the natural and scientific values of this region, the Environmental Protection Area (APA) was founded.
Most extraordinary is the quartzite karst of the area. Quartzite is normally not soluble by water, so it does not allow the formation of karst. But here, with high tropic temperatures, frequent rains and much time, the nearly impossible happened, the quartzite was dissolved. The Gruta do Centenário is 3,790 m long and 481 m deep. It is the longest and the deepest quartzite cave of the world.