My fascination with these opals comes from their complex patterns and endless variety. Here, the matrix and fire can be seen as reflections on a ribbon-like surface surrounding its central eye. These patterns probably formed in a manner similar to that for agates, since both consist of mineral precipitation within a fluid-filled cavity. About 80 pictures in the book Canteras, Mexican Opals in Matrix show agate features.

Canteras are Mexican opals in matrix. Some have features similar to agates, probably because they also form within cavities in matrix. These pictures show how the fire varies with angle of view. This opal appears to have goethite-coated rutile crystals in it, but I’m a novice for crystal identification. Many pictures like this are shown in my book, Canteras, Mexican Opals in Matrix. Slideshows are also at www.mudpot.com .

Jack Hobart