New explorations at the Stoneham, Colorado, barite locality

Stoneham in northeastern Colorado is known throughout the world for its occurrence of stunning blue barite crystals. The barite at Stoneham occurs in a bed rich in montmorillonite clay, derived from alteration of volcanic ash, in the Chadron Formation of the White River Group of Oligocene sedimentary rocks. The barite crystals, as much as 4-6 inches long, crystallized from ground water within open pockets that formed by movement along a northeast-dipping reverse fault that cuts the clay bed. -from Authors