This is a stunning, cone shaped, naturally shiny Jequitinhonha Agate, also know as Amazon River Tumbled Agate, from Brazil.
Brazilian River Agates are naturally polished surface agates. The agate is polished by being located in a moving flow of water and small minerals, diamond dust and sand. The agates sometimes roll downstream as well, adding to the polished finish appearance.
These rare agates are often called "Slick" Agates in reference to their shiny exterior finish. At first glance you may think these are sealed or acrylic coated but that is not the case, these are naturally occurring agates that are found in rivers and streams, especially those coming down from mountainous areas where there is turbulent water flow over the rocks. In the sands of some of the rivers, including the Jequitinhonha River located in Minas Gerais, Brazil, there is diamond dust as well as diamonds, over thousands of years, the river agates became naturally polished by the diamond dust resident in the sands of the rivers.
We believe that it is no longer legal to "mine" these amazing Agates. We purchased this one and a few others from a Brazilian Wholesaler who has had hundreds of these just laying in his yard for the past 20 or so years...