Platinum dendrites were found in lithium tetraborate crystals grown by the Czochralski method using a platinum crucible. The mode of occurrence and formation mechanism of platinum dendrite in lithium tetraborate were examined. It is revealed that platinum dendrites developed in the cellular structure that occurred during growth. The formation of platinum dendrite that is discussed is associated with the growth condition leading to cellular growth. The morphology of platinum dendrite is also explained by its specific crystallographic symmetry.