concretion

That’s because the concretions there are partly made of an iron-carbonate mineral called siderite that only forms in low-oxygen environments.

Most concretions in other fossil beds have no fossils or fossils that are just bones and hard parts, but “Mazon Creek has really good, soft-tissue preservation inside these concretions,” she says.

While we don’t completely understand how concretions form, all the evidence so far is that it’s the concretion itself that is the preservation force keeping things from decaying away.

Fossils from this deposit are preserved within concretions made of an iron carbonate mineral called siderite.

A concretion of rounded quartz pebbles, cemented by ferruginous matter, apparently of recent formation.

In the first place, what common element is there in matter, form, and the concretion of matter and form?

Phleb′olite, a calcareous concretion found in a vein; Phlebol′ogy, science of the veins; Phleb′orrhage, venous hemorrhage.

Again, The concretion of Ice will not endure a dry attrition without liquation; for if it be rubbed long with a cloth, it melteth.

And many bodies will coagulate upon commixture, whose separated natures promise no concretion.