Housed in the former Palácio dos Governadores at the top of Praça Tiradentes — the building that defined the upper edge of the square in colonial times and now belongs to the Federal University. The science museum, run by the famous School of Mines, holds one of the largest mineralogy collections in Latin America: about 25,000 specimens, from tiny diamonds to room-sized geodes.
It is more engaging than a list of rocks suggests. The displays trace the geology of the Minas Gerais gold rush — what people were digging for, why they found it here, how it shaped the town. There are also sections on astronomy, metallurgy, and historic surveying instruments. Good for an hour; longer if you have any interest in earth science.