“Algar do Carvão” is a volcanic pit with a peculiar genesis, including both silicic formations and basaltic products dated of 3,200 and 1,730 years ago, respectively. This 90 m depth pit, presents unique features and environmental importance, especially due to its unique speleothems of amorphous silica.It is in the top ten worldwide volcanic cave in terms of mineral deposits (silica speleothemes).