Drow Lance

The Drow Lance is an enchanted spear +3 which dissolves to Adamantine Dust when taken outside the Underdark, like all drow equipment.

Baldur's Gate II: Shadows of Amn

 * Ust Natha - Temple of Lolth

In-game description
"One of the earliest weapons, dating back to the most primitive of times, the first spears were simply wooden poles of sticks sharpened at one end. This drow lance is a superior version of the traditional spear, often used by drow foot soldiers.

This item, list most drow equipment, is created using adamantine, an alloy of adamantite that quickly turns into dust if removed from the Underdark."