A limb cast is when the outside of ancient wood was buried under such high pressure and temperatures that the outer layers were preserved but the interior of the wood had burned away and filled in with other minerals, not retaining the wood cell structures. Petrified wood is when the cell structure of the original wood stays in tact because it experiences slow mineral replacement as opposed to the rapid replacement in a limb cast. This appears to be a mixture of the two where gorgeous sparkly calcite crystals are growing out of the back and can be seen throughout. Face polished to a beautiful shine for display. Illinois. Hand mined, ethically sourced.
