Amethyst geode with large calcite crystal

An amethyst geode from Uruguay, with a striking large calcite crystal growing within its violet interior wall. A two-generation mineralogy, in which the carbonate phase is impressively documented after the quartz phase.

Amethyst first crystallized in the lava geode from silica-rich solutions over millions of years. Only then did calcium carbonate-bearing solutions penetrate the remaining cavity, in which the prominent calcite crystal could grow into its trigonal scalenohedral form.

The size of the calcite crystal is unusual. Typically, several smaller calcite scalenohedra form; a single large crystal requires stable solution conditions over long crystallization periods in a sufficiently large cavity.

Uruguayan material from the Artigas Basin is considered one of the premium amethyst deposits worldwide. Accompanied by prominent calcite crystals, it is valued in the collector's trade as a didactic showpiece because it makes the geological stratigraphy of geode genesis visible.

A collector's item with a clear mineral sequence and a visual focus on the calcite crystal.