The Oco geode (also spelled “ocho”) is a small but striking geode found in Brazil in a remote area known as Tres Pinheiros (Three Pines) near the southern border at an elevation of 3,000 feet. This area’s geological history, characterized by volcanic activity and lava flows, provides the perfect conditions for the formation of these tiny geodes.
Key Takeaways
- The Oco geode is a small geode found in southern Brazil, formed in basalt from ancient volcanic activity.
- Most Oco geodes range from 1 to 3 inches and are collected from weathered soil or extracted directly from rock.
- These geodes often contain quartz and amethyst crystals, making them popular with collectors.
- A thin shell and distinctive rope-like exterior help identify an oco geode.
- Many collectors value Oco geodes for both their natural beauty and their association with balance and tranquility.
Finding Geodes
Most Ocos are found in the dark red-brown soil produced from the weathering of the basalt rock in which they formed. Other Ocos are chiseled directly out of the basalt rock.
In the off-season, farmers plow their fields to find these tiny geodes. The geodes are collected and transported down the mountains in burlap sacks and buckets, where they are sold “as is” to be cut or cut and polished to be sold.
There are multiple theories about where Oco geodes got their name. One is that they are named after the Orinoco River, the other is that their name comes from the Portuguese word for “hollow.”
Oco Geode – Internal Structure
Even though most Ocos are small (one to three inches), they are attractive to collectors, along with Las Choyas geodes and trancas geodes, for the secondary mineral formations they contain. The crystals found within these geodes vary in composition but often include minerals such as quartz and amethyst.
Oco geodes have two distinguishing characteristics that make identification easy. The outer chalcedony shell is rope-like and when the internal chalcedony layer is exposed, it shows swirling “flame-like” patterns. They also have a very thin shell. Care must be taken when they are cut and polished.
Richard Gross
Tranquil Oco Geodes
Believers in the power of crystals associate Oco geodes with harmony, balance, and a sense of tranquility.
Richard Gross
FAQ: Oco Geode Guide
What is an Oco geode?
An Oco geode is a small, hollow stone formed in volcanic rock, typically lined with crystals such as quartz or amethyst. They are especially known for their thin shells and striking internal patterns.
Where are Oco geodes found?
Oco geodes are found in southern Brazil, particularly in the Tres Pinheiros region near the border with Uruguay. They are commonly collected from soils formed by the weathering of basalt.
How big are Oco geodes?
Most Oco geodes are quite small, typically measuring between 1 and 3 inches in diameter. Despite their size, they often contain well-formed crystal interiors.
What minerals are inside an Oco geode?
The most common minerals found inside an Oco geode are quartz and amethyst, though variations in crystal structure and color can occur.
How can you identify an Oco geode?
An Oco geode can be identified by its thin outer shell, rope-like exterior texture, and the swirling, flame-like patterns visible in the inner chalcedony layer when cut.
The Oco geode may be small, but its geology and crystal beauty make it a standout among collectors. From Brazil’s basalt fields to display shelves, these tiny geodes continue to captivate.
This story about the geology of the Oco geode previously appeared in Rock & Gem magazine. Click here to subscribe. Story by Richard Gross and Pam Freeman.
