What is the most common geode found in Brazil?

Answer 1

Geodes can form in any cavity buried. These wells are usually gas bubbles inside of igneous rocks, pockets under tree roots, vesicles in lava after a volcanic eruption or even animal burrows. Over time, the outer wall of the cavity hardens, and dissolved silicates and carbonates deposited on the inner surface, the slow feed of mineral constituents from groundwater or hydrothermal solutions allows crystals to form inside the hollow chamber. Over millions of years after its formation, the geode returns to the surface through normal geologic processes.

The size of the crystals, and their form and color are variable, making each geode unique. Some are clear as quartz crystals, and others have rich purple amethyst crystals. Others can have agate, chalcedony, or jasper. You can not say how the interior of a geode until it is cut or broken, so as to expose its interior.

They are common in some rock formations of the United States, Namibia, Mexico and Brazil.