They may be one of the most common of all the geodes, almost ubiquitous in any number of rock shops, trinket stalls, museum gift shops etc. – but that shouldn’t blind us to what amazing things they are. Their delicacy and patterning is unique, washed through with gorgeous feathery ‘cloud agate’. This plus the complex crystal caves filled with everything from Amethyst to Goethite and beyond make them possibly one of the most remarkable agates in the world when at their best – and I don’t say that lightly.

For all their ubiquity, it is surprisingly hard to find information about these, maybe partly since nobody can agree on the exact name. I have seen Oco, Coco, Ocho, Ocos etc. Oco is the name given on the Mindat website, so I will go with that one for now. However, I only recently became aware of the fact that there is possibly more than one Brazilian location involved. The classic Oco comes from Três Pinheiros, Fountoura Xavier, Rio Grande do Sul. These stones are dug out of the red-brown earth of the region and form a welcome extra ‘crop’ for the farmers. The following though, is almost certainly a Parana Cloud Agate – Similar but subtly different:

Like a lot of the stones out of Brazil, there is a certain vagueness about their origin – and I can’t pretend to know much at all.  But I am totally blown away by the delicate patterns and sheer intricacy of these stones.  I have now launched a gallery of them in the ‘non-thundereggs’ section of the website.