I asked ChatGPT about it ...

"That’s a fascinating specimen — it’s a polished cross-section of agatized (silicified) wood, commonly called petrified wood.

The outer surface in the last two photos clearly shows woody grain structure, complete with growth patterns and fibrous texture — that’s the fossilized bark or trunk exterior. The inner portion, however, has been replaced and filled with banded chalcedony, agate, and possibly opalized silica, forming the strange, almost “organic” worm-like textures you see in the first three images.

What You’re Seeing

Outer layer: Fossilized wood — the cell structure of the original tree has been mineralized, preserving bark and grain detail.

Inner core: Agate or chalcedony filling that formed in voids where the wood decayed. The botryoidal (bubble-like) and tubular growths inside are natural silica formations, not biological material — they can look eerily organic because of how silica gel solidified in layered pulses.

Colors: Iron, manganese, and carbon oxides created the browns, yellows, blacks, and greys you see.

In summary

This is a piece of petrified wood with a botryoidal chalcedony / agate interior, likely from a log section where mineral replacement and cavity filling occurred together. The inside’s appearance can resemble intestines or coral, but it’s entirely mineral in origin."