Calcite

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A set of two gemmy cleavage rhombohedron's of calcite. These exhibit the double refraction property. Size provided for the larger of the two examples.The Challenger Cave system, a series of seven caverns located near Monterrey in Nuevo Leon, Mexico, was formed within Cretaceous limestone beds through karst dissolution by groundwater. Over time, calcium carbonate-rich fluids slowly precipitated large calcite crystals within these subterranean cavities. Historically, this cave system served as a key source for clear calcite specimens that, when cleaved along natural planes of weakness, yield perfect rhombohedrons. These rhombs display high optical clarity and exhibit strong double refraction, a physical property where light entering the anisotropic crystal lattice splits into two distinct rays traveling at different velocities, causing any image viewed through the crystal to appear doubled. Additionally, these specimens are studied for their distinct fluorescent properties, showing a pink reaction under longwave ultraviolet light and a blue phosphorescent afterglow under shortwave ultraviolet light.