rare dark amethyst geode with a large calcite crystal sugared with black goethite crystals

A rare dark amethyst druse from Uruguay with a large calcite crystal, encrusted with black goethite crystals. Three minerals in documented growth stratigraphy.

The goethite encrustation on calcite is a rare three-mineral constellation. Goethite, an iron hydroxide with the formula FeO(OH), grew as a later phase as a microcrystal aggregate on the already grown calcite faces. Such successional growth stratigraphies are a premium detail for collectors.

Uruguayan amethyst is considered the darkest, most deeply violet-colored amethyst variety worldwide. The Uruguayan deposits in Artigas and Salto supply this material from the Arapey Basalt Formation.

The combination of dark premium color, large calcite inclusion, and goethite encrustation is a rarity in the worldwide collector market due to its specific find. A three-mineral genesis in a display-case dimension.