Amethyst geode

An amethyst geode is an underground structure found in Overworld biomes. Amethyst geodes contain smooth basalt and are the only source of calcite and amethyst items and blocks.

Generation
Amethyst geodes generate commonly between Y=70 and the bedrock layer regardless of whether "generate structures" is toggled on or off. Each chunk has $1/53$ chance to generate a geode. They override only caverns and mineshafts. Sometimes they are exposed on the surface, such as on beaches and underwater in oceans.

Structure
[[File:Amethyst geode.png|thumb|The inside of a cracked amethyst geon.