Drow Crossbow of Speed (Drow Crossbow of Speed +3 in-game) is an enchanted light crossbow +3 in terms of enchantment. Like all adamantine items, this will turn into Adamantine Dust when it's taken out of the Underdark.
This weapon is nearly the same as the Light Crossbow of Speed, but since the mentioned crossbow is a +1 weapon, the drow variant weapon with +3 bonus to damage and -3 THAC0 with a speed factor of 1, is a lot better. But the +1 crossbow isn't made of adamantine and therefore can be used anywhere.
|“|| Drow Crossbow of Speed
A crossbow is a bow mounted crosswise on a wooden or metal shaft, the latter called a tiller. The bow is usually made of ash or yew. The crossbow fires a quarrel (also called a bolt). This item, like most drow equipment, is created using Adamantine, an alloy of adamantite that quickly turns to dust if removed from the Underdark.