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Marcasite in Agate is one of the most visually dramatic and geologically fascinating materials I cut, combining the translucent, banded beauty of agate with the metallic, mirror-bright inclusions of marcasite crystals that catch light like tiny embedded stars. Each cabochon I shape from this material is a study in contrast, where the warm, glowing depth of the agate host stone is punctuated by the cool, silvery flash of the marcasite, creating a finished piece that reads as both organic and otherworldly at the same time.
Marcasite is an iron sulfide mineral that crystallizes in the same chemical composition as pyrite but with a different crystal structure, producing the characteristic brassy to silvery metallic luster that makes it so visually striking when preserved within an agate matrix. The combination forms when marcasite crystals develop within silica-rich cavities at the same time as the surrounding agate is depositing, locking the metallic inclusions permanently within the translucent stone in formations that range from scattered specks to dramatic radiating clusters.