Small Polished Oco Geode Slices Uniqueness Guaranteed: Every item is one-of-a-kind, making them ideal for all projects or designs. Avg Size Range: (1 To 2.5 Inches) Sizes Vary Material Origin: (Brazil) Oco geodes form when groundwater deposits sediment and other minerals like quartz inside basalt pockets, which then seal over. These minerals harden in a similar process to agate, and the basalt eventually wears away to leave the geode behind. When cut open and polished, these geodes display colorful wavy patterns along the rim. Custom Requests: Have specific preferences? Leave a message with your order, and we'll do our best to accommodate your requests if possible. Handmade items vary in size, shape, and color when selected randomly (the highest quality items are chosen first). They'll be as beautiful as those in the photos.