Portuguese for “hollow,” Oco Geodes are found in the steep hills of Tres Pinheiros in the state of Rio Grande do Sul, Brazil. Ocos can range in size from one inch up to five or six inches in diameter. Quartz crystals commonly line the inside of these spectacular geodes, and rarely the crystals are amethyst. Many of the Ocos contain black needle-like crystals (probably goethite) among the quartz. Ocos are easily distinguished by their “rope-like” surface on both the inside and outside of the geode. When cut and polished, the rims display prominent white wavy or flame-like patterns similar to their Trancas geode cousins.