Could a species that naturally produces an obsidian/flint like material exist ?
Or to put it more accurately could an obsidian/flint like material that is purely of biological origin (and not the result of naturally occurring volcanic or lightning activity) exist ?
If so what would it look like ? I mean by this what type of creature/species/family would this characteristic be most likely/implausibly to evolve out from ?
I'm assuming that this is COMPLETELY IMPOSSIBLE in real life but if we were to take a much more unrealistic and fantastical approach what would be the most quasi-plausible way to go about this ?
I'm thinking some kind of fantasy underwater giant coral-like species could do the trick ?
Or perhaps a mammal/reptilian/land-based creature that would excrete huge amounts of feces that would turn into an obsidian/flint like substance upon coming into contact with the air/solidifying ?
Or why not simply both at the same time, they could potentially occupy different ecological niches but produce a similar substance ?