Uraninite is a mineral primarily composed of uranium dioxide (UO2) and is the most significant ore of uranium. It typically appears as black or brownish-black in color and has a metallic luster. Uraninite is often found in granitic rocks and can also contain trace amounts of other elements, such as thorium and lead. This mineral is important in the field of nuclear energy, as it is a primary source for extracting uranium used in nuclear reactors and weapons. Due to its radioactive properties, uraninite must be handled with care to minimize exposure to radiation.