Black Ganesha statues are often made in stone such as granite, black marble, or basalt, or made with brass and iron and layered with a black patina. Black stone commonly occurs in Rajasthan, Andhra Pradesh, Tamil Nadu, Karnataka, and Kerala, where temples and homes house dark-hued Ganesha idols, which are worshipped with devotion by locals. https://www.exoticindiaart.com/blog/is-black-ganesha-good-or-bad/