Very rare dark amethyst with large calcite as cannon spar with black goethite crystals

A very rare dark amethyst from Uruguay with large calcite "cannon spar" and black goethite crystals. Three minerals in one geode, an extraordinary succession constellation.

Cannon spar is a specific calcite growth form with distinctly thick, columnar crystals that resemble cannon barrels. Such calcite forms are a find-dependent collector's characteristic.

Goethite (iron hydroxide, FeO(OH)) as a later mineralization phase grew black on the already grown calcite cannon spars. Three-mineral succession: amethyst, then calcite, then goethite.

Uruguayan amethyst is considered the darkest, most deeply violet-colored amethyst variety worldwide. The constellation of dark premium color, cannon spar, and goethite frosting achieves the highest collector classification.

A museum-worthy Uruguayan collector's item with three-mineral genesis and top gemological classification.