Botryoidal Geode!

A geode is a hollow, usually spherical rock, that when broken open reveals a cavity lined with crystals or other mineral formations. Here are some key points about geodes:

Formation: Geodes form when gas bubbles or cavities in volcanic or sedimentary rock are filled with mineral-rich water. As the water evaporates, it leaves behind minerals which crystallize over time, lining the inside of the cavity.
Structure: The outer layer of a geode is typically rough and nondescript, often making it look like an ordinary rock until it's cracked open. Inside, you might find crystals like quartz, amethyst, calcite, or even rarer minerals.
Location: They are commonly found in regions with volcanic activity or limestone deposits. Famous locations include parts of the United States, Brazil, Uruguay, and Mexico.
Uses: Geodes are popular among rock collectors and are often cut and polished for use in jewelry or as decorative pieces. Some are also used in metaphysical practices for their supposed healing properties.