#pyritized fossils

I ended up going down a rabbit hole of "organic/biogenic gemstones" this week. So, let's look at what I found! Starting with...

Opalized Fossils (aka Opal Replaced Fossils)

Bones, teeth, shells and plant material turned to opal, embedded in the ancient claystone and preserved, like the gemstones, for 100 million years under a thin veneer of sediment. [source]

Pyritized Fossils

Pyrite—often called “Fool’s Gold”—is an iron sulfide mineral that, under rare geochemical conditions, can coat or even replace prehistoric organisms, transforming them into luminous, gold-toned fossils. These pyritized fossils are among nature’s most striking creations, uniting chemistry, time, and artistry in a single form. [source]

Ammolite

It is made of the fossilized shells of ammonites, which in turn are composed primarily of aragonite, the same mineral contained in nacre, with a microstructure inherited from the shell. It is one of few biogenic gemstones; others include amber and pearl. [source]

Agatized Coral Geodes

Agatized Coral forms when silica replaces the original calcium carbonate skeleton of a coral colony. This replacement process creates beautiful specimens with cave-like appearances. [source]

Amazing! And though I'm not a gemstone person, I really want some now!!