a person with a fossilized mind
How to describe a person who have a fossilized mind?
whatever he hears he will not (get it into one's head)
Close-minded
not willing to try new things or consider other opinions
Also spelled as closed-minded
Also consider ossified
having become set and inflexible
Alternatives are
- stubborn
- bull-headed
- pig-headed
- narrow-minded
- hard-headed
You may be thinking of "thickheaded":
thickheaded — (of a person) dull-witted; stupid
The connotation is one of stupidity or inability to understand something:
Alice is so thickheaded she couldn't understand the instructions you sent to her.
Bob is pretty thickheaded so you may need to use small words.