An orbicular bead is a round piece of stone that it is formed in particular environmental conditions, usually in granitic layers of rock.
The orbicular granite in Unpyeong-ri contains a lot of diorite that is believed to have formed when magma rose to the earth’s surface during a massive diastrophism in the Korean Peninsula about 2.3 million years ago.
Eight groups of granite boulders were discovered in Ungok-ri valley in Unpyeong-ri, to the southeast of Sangju, six of which are submerged below the water of the valley while two lie exposed above the water.
Villagers refer to these granite boulders as 'turtle rocks' because of their supposed resemblance to turtle shells.
Each orbicular bead has a diameter of 5-13 centimeters and a black edge.
This kind of stone is only found in some 100 locations around the world.
The orbicular granite found in Unpyeong-ri is a geologically rare material of considerable value to studies on the formation of rock.
They have been designated and conserved as Natural Monument (No.69) as they provide important data for research on the composition of rock.