Polonium is a metallic element, and its lustre is described as silvery-white. However, it's important to note that:

* Polonium is highly radioactive and extremely dangerous to handle, so its lustre isn't easily observed in practice.

* It tarnishes quickly in air, further complicating its visual assessment.

Therefore, the silvery-white lustre is more of a theoretical description based on its metallic nature rather than a commonly observed characteristic.