燕石为玉 (燕石為玉) yān shí wèi yù

yān shí wèi yù set phrase treat a stone from Yan like jade
Domain: Idiom 成语
Notes: An ideiom from a traditional story where a person from Song found a rock from the state of Yan and believed it to be a precious gem (Guoyu '燕石為玉')