Lake Superior Agate ex Houran Coll.

Item Description

An exceptional and rare Lake Superior "eye" agate from Minnesota, meaning a concentrically banded pattern within that gives the appearance of an eye. The polished face has a striking large centered pattern, and is apparently large for this material. The blue in the center moving to grays and finishing with white rings is desirable and makes this piece very special. The eye is surrounded by classic Lake Superior reddish-brown agate. The front and back have been carefully polished. Nearly flawless with few imperfections or fractures as most agates have. It was recently found in Duluth, and was in the USA classics gem and minerals collection of Jim Houran. More info here from an anonymous friend and agate-afficionado: 

Short version: Concentrically banded agates (the things most people think of when they think of agates) will of course show roughly eye-shaped patterns if cut across the banding, Lake Superior agates, having been worn out of the basalt matrix and dragged around the upper midwest for millennia by the glaciers, often show such features even without cutting. What are usually called "eyes" in agates are typically a surface feature, formed as hemispherical or semi-hemispherical blobs near the outside of the bubble in the basalt (in the case of Lake Superior Agates - not all agates formed in basalt) that later (or contemporaneously) completed the rest of the agate formation. Think of how malachite sometimes forms such concentric-looking hemispheres on a matrix before getting covered by layers of banded malachite. Another feature that sometimes looks like an "eye" is a "tube" if erosion or a cut has you looking straight down at the tube, end-on.