* Geologic Formation: The specific name would depend on how the rock formed. Here are some possibilities:
* Geode: This is the most common term, but technically geode implies a cavity lined with crystals that is formed within a volcanic rock.
* Vug: A vug is a small, irregular cavity in a rock, often lined with crystals.
* Druse: This refers to a cluster of crystals, often found lining a cavity.
* Nodule: A nodule is a rounded mass of mineral matter, sometimes containing a cavity with crystals.
* Specific Crystal Type: If the crystals lining the cavity are of a particular type, you might use that type in the name. For example, "amethyst geode" or "quartz vug".
* Descriptive Terms: You could use descriptive terms like "hollow rock with crystals", "crystal-lined rounded rock", or "crystal-filled cavity" to describe it.
To give you a better answer, I need more information!
Please tell me:
* What kind of rock is it? (e.g., volcanic, sedimentary, metamorphic)
* What type of crystals are inside?
* Where did you find it? (e.g., desert, beach, mountain)
With more details, I can help you find a more specific and accurate name.
