large geode with Marienglas crystals, very clear selenite crystals and pink anhydrite from Brazil

A large geode with selenite crystals and pink anhydrites from Brazil, Rio Grande do Sul. Glass-clear selenite plates stand next to pastel-pink anhydrite aggregates, both calcium sulfate modifications in a single cavity.

Selenite (CaSO₄·2H₂O) and anhydrite (anhydrous CaSO₄) are two polymorphic calcium sulfate modifications that crystallize under different water availability conditions. The constellation in a geode documents changing solution conditions over the growth phases.

Pink anhydrites with selenite in a single geode are a top collector's item due to the deposit. The Rio Grande do Sul deposit provides the highest quality material worldwide for such multi-sulfate constellations.

Selenite is soft (Mohs 2) and water-soluble; cleaning should only be done dry. The gallery dimension demands its own museum display case.

A Brazilian museum-quality collector's item with two-sulfate genesis, gallery dimension, and top classification.