AMETHYST WITH CALCITE
Ametista do Sul is, true to its name, recognized as the amethyst-producing capital of the world. Here we have deep purple amethyst crystals, displaying an unusually rich saturation reminiscent of Uruguayan material, forming a complete carpet across the specimen's face. These are dramatically accented by exceptional calcite crystals reaching 12 cm, their gem-like transparency creating a striking contrast against the amethyst backdrop. While specimens from this prolific region are well-known, this particular piece stands several cuts above the norm, possessing the size and aesthetics to command center stage in any serious mineral display.
More info:
The mineralization sequence in Ametista do Sul's basalt cavities proceeds in distinct stages. Initial hydrothermal fluids deposit celadonite, followed by primary quartz crystallization. Subsequent radiation-induced oxidation of iron within the quartz structure produces amethyst. The final phase introduces calcium-rich solutions, resulting in scalenohedral calcite precipitation on amethyst surfaces. This low-temperature hydrothermal process (<100°C) occurs within vesicles in the host basalt, forming geodes that frequently exceed two meters in diameter. The deposit represents a classic example of successive mineral precipitation within basaltic host rocks.