Amethyst geode

Amethyst Geode is an underground structure that is the only source of Amethyst Crystals, Tuff, and Calcite.

Overview
The Amethyst Geode generates rarely underground, and can generate anywhere between sea level and bedrock. It overrides cave and ravine generation but not abandoned mineshafts as well as other structures.

The Amethyst Geode consists of a hollow shell of Blocks of Amethyst with Budding Amethyst blocks randomly generated throughout. Amethyst Crystals will generate within the structure on any amethyst block. Surrounding the amethyst is a shell of Calcite, which itself is surrounded by a shell of Tuff.