I would venture a guess that what you have here is a nice Fulgurite deposit.
This can happen when a tree is struck by lightning,
it eventually kills the tree and can leave a healthy deposit underneath.
Some can fuse with mineral deposits and even create something new...Or uncharted.
"When lightning strikes a tree, the ground typically explodes out, and the surrounding grass dies, forming a scar and sending electric discharge through nearby rock, soil and sand, forming fulgurites, also known as 'fossilized lightning'," Pasek said.
~ Apr 12, 2023
Source ~
See the newly discovered fossilized material left behind by a Florida lightning strike