Fossilized
Part of speech: adjective
Definition: In a state of fossilization; preserved in rock.
Inflexible
Part of speech: adjective
Definition: Not flexible; not capable of bending or being bent; stiff; rigid; firm; unyielding.Not willing to change, e.g. one's opinion or habits; obstinate; stubborn; resolute; determined.
Example sentence: Public school teachers enjoy a huge amount of job security, thanks to their powerful unions and inflexible work rules.