Definition

Noun: 1. (Mineralogy) A hollow, rounded rock formation or nodule, the internal cavity of which is typically lined with a layer of inward-pointing crystals, such as quartz or amethyst. Geodes form when mineral-rich water deposits crystals inside a gas bubble within volcanic rock or another cavity.

Usage

Geodes are geological objects studied in mineralogy and collected as natural curiosities or for their aesthetic crystal interiors. * The geologist cracked open the geode to reveal the beautiful amethyst crystals inside. * This museum has an impressive collection of large quartz geodes from Brazil. * Finding a geode on our hike was a exciting surprise.

Advanced Usage

• Geodic (adjective): Having the form or characteristics of a geode.
  • The geodic structure of the rock suggested it might contain crystals.

Variants and Related Words

• Thunderegg: A specific type of geode found in rhyolitic lava flows, often filled with agate or chalcedony.
• Nodule: A small, rounded lump of a mineral or other substance, which can sometimes be hollow like a geode.

Synonyms

• Cavity crystal
• Crystal-lined nodule

Antonyms

• Solid rock
• Massive mineral specimen (A mineral formation without a hollow center)

Noun

1. (mineralogy) a hollow rock or nodule with the cavity usually lined with crystals