4.25" Stunning Polished Black River Agate - Argentina

Black River agate is a lesser-known gem and mineral specimen from Argentina. Most specimens feature white, brown, blue, and beige banding, though colors and tones can vary lighter or darker. These agates have relatively subdued coloring compared to other Argentinian agates, but the contrasting colors create excellent separation between the swirling bands. The beauty of Black River agates increases with every pass of the eyes.

Experts estimate that these agates are Brazilian in origin, but were deposited by flooding and altered sea levels into Argentinian rivers. The current consensus is that agates from Argentina are Permian in age. They are a relatively new discovery, only known outside of Argentina since the early 1990s, along with Condor and Puma agates. All of the Argentinian agates make wonderful additions to any mineral collection, and Black River agates are no exception.

The Wegeler effect, also known as the shadow effect or parallax effect, is a three-dimensional oddity in which rotating a banded agate creates the illusion that those banding lines move. One line will move with the source of light while the other moves with your point of view. This occurs in agate that has tightly packed, alternating bright opaque bands and transparent bands.