Nature is a rich source of technologically relevant materials, such as diamond, one of the hardest known materials, or graphite as a suitable precursor of graphene. This list has now gained a new member belonging to the new class of topological insulators (TIs). The surface states of TIs display a linear dispersion combined with spin polarization due to spin-momentum locking, which opens intriguing application perspectives in spintronics. We have found that the mineral Kawazulite with the general chemical composition Bi2(Te,Se)2(Se,S) is a natural TI whose electronic properties compete well with its synthetic counterparts. Based on this discovery, natural TIs may exist in other minerals, which due to their minimized defect densities display even better electronic characteristics.