Osuk that is produced in Ungcheon is black like a feather of crow and glossy. And the quality is excellent. So it is used as the material for various epitaph, tomestones, etc. As you trim stone more and more, the black color becomes distinguished, and as you carve, the white color comes out. Especially Osk from Seongjusan Mountain area is famous as the best quality in Korea and is the indigenous property of Boryeong.