Seems to be cheaper than iron. Less complicated than boiled leather. And certainly hard enough to dull a blade.
Yet I almost never hear of any civilization using it?
Yes, people did use stone armour. Here is a picture of a stone armour used in the Qin dynasty of China (2nd century BC):.
https://commons.wikimedia.org/wiki/File:Qin_stone_armour_suit.jpg
You can see it's basically stone slabs being strung together. It seems quite bulky and heavy. Metal is easier to manufacture with molds, lighter while still hard, and not as easy to shatter.
How are you proposing that it would be utilized? Sown into leather? Tied on with ropes? Do you have any examples of what you're talking about?
