Half a Thunderegg!

This rock appears to be a type of **thunder egg** or **agate**. Here's why:
1. **Coloration and Banding**: The rock shows a combination of colors, including brown, white, green, and possibly some hints of other colors, which is typical for agates and thunder eggs. The banding pattern is also characteristic of agates, which form in cavities of volcanic rocks.
2. **Translucency**: Some parts of the rock are translucent, which is common in agates due to their chalcedony composition.
3. **Texture**: The rock's texture looks somewhat waxy or glassy, which is typical for agates that have been polished or naturally worn smooth.
4. **Inclusions**: The yellowish or brownish areas could be due to iron oxide or other mineral inclusions, which are often found in agates. Thunder eggs are nodules of agate found in volcanic rocks, and they often have a hollow or partially hollow interior filled with crystals or banded agate.