just discovered a new-for-me term relating to fossil organic materials = Organics being a particular field of bead interest of mine-
Taphonomy !
its important because it covers the processes or stages of decay in animal or vegetable origin matter- between the living state and the decaying or mineralising of matter as it becomes fossilised, petrified, opalised, crystallised, calcified, etc.

so - the current discovery that coral is getting bleached of its redness (due to warmer and polluted oceans) is turning it into what appears to be absorbent fossil coral?
real hard fossil coral may not be red but is rock-like and has no holes and has hardened over centuries?
study of Taphonomy gives evidence of age...