Dolomite with Chalcopyrite

Unknown Owner

An aesthetic example for this locality, a finger of matrix covered by lustrous pink rhombohedral dolomite crystals and small crystals of chalcopyrite. This is in terrific condition all around.The quarries around Black Rock, in Lawrence County, Arkansas, are situated within the Ozark Plateaus geomorphic province. Geologically, this region is characterized by the Ordovician-aged Plattin Limestone and Joachim Dolomite formations. These sedimentary layers were deposited in a shallow marine environment roughly 450 to 485 million years ago. The distinctive pink color of the dolomite in this area is attributed to trace amounts of iron or manganese that replaced magnesium within the carbonate crystal lattice during diagenesis or later hydrothermal activity. Historically, these quarries have been operated since the early 20th century, primarily for industrial crushed stone, railroad ballast, and agricultural lime. However, the locality gained a specialized reputation among mineralogists when eagle-eyed quarry workers and collectors began rescuing high-quality crystallized specimens from the primary crushing operations.