Mining in the United States for precious gems can be a fun and rewarding experience, especially when it comes to learning about mineral formations. One gemstone in particular, the emerald, is sought after for both rarity and beauty. The rare aspect is dual-fold, in that concentrations of emeralds are not very common, but also because finding facet-quality emeralds is even more rare. For example, the raw emerald specimen from North Carolina pictured here demonstrates how the formation can be a limiting factor in the size of emerald crystals.
Emeralds are a possible byproduct of hydrothermal processes when conditions and chemical composition are optimal. The way to envision this is to imagine hydrothermal fluids under extreme pressure being forced to the surface and pushed through rock cavities by water or magma. When the catalyst recedes, hydrothermal fluids are left in the rock cavities to cool and form emerald crystals. Emeralds created under these conditions in crevices and rock fractures, which means jagged fractures largely determine the size of emeralds formed.
Clarity is another factor in the rarity of emeralds. The deposits might be in proximity to calcite and other minerals which may cloud the hydrothermal fluid. This specimen demonstrates a ratio of clarity, where the majority of emerald crystal is foggy and opaque, while only a small fraction is clear enough to allow light to pass. Stripe patterns from internal crystal fractures are visible throughout the crystal material. Emerald can be surprisingly fragile and it's possible cracks in the crystal are the result of increased pressure or rapid cooling during the solidification phase.
The specimen also reveals how the shape of rock cavities and fractures play a role in the formation of emerald crystals. Edges of this crystal have been rounded and slightly polished to reduce further chipping or fracturing when handled as a demonstration piece. The monetary value of the specimen is quite low without a complete raw formation and the lack of sizeable pieces with clarity for faceting, but it is still a beautiful gemstone to have in the collection.
