Native ſilver is ſometimes inherent in petrefactions, but never, to my knowledge, conſtitutes the ſubſtance of them, unleſs mineralized with copper and ſulphur.
Quickſilver in an organic Form.
When mineralized by ſulphur, it ſometimes, though very rarely, conſtitutes petrefactions.
Copper with an organic Form.
Bones and teeth are ſometimes found replete with the blue calx of copper. Bits of copper pyrites often ſtick in petrefactions, but ſeldom conſtitute their whole ſubſtance. I have some such from Norway, in a matrix of magnetical iron ore.
Iron with an organic Form.
Calciform iron ſometimes is found in the ſhape of roots and branches of trees. When mineralized by ſulphur, it frequently exiſts in petrefactions, but ſeldom conſtitutes the whole maſs.