great lilac-colored amethyst geode with freestanding calcite from Brazil

A lilac-colored amethyst geode from Brazil with a freestanding calcite crystal inside. The calcite is coated with a fine layer of small rock crystals and forms the unusual center of the geode.

Such co-mineralizations occur when the cavity solution alternates between carbonate and silicate phases. The sugared calcite documents a late quartz precipitation over the already grown carbonate single crystal.

The edge of the geode consists of chalcedony and rock crystal. The lilac-colored amethyst crystals inside are natural and highly lustrous. A mineralogically dense collector's item with documented co-mineralization.