Craft Crystal Weapon( Oriental Adventures, p. 61)
You can create magic weapons from Kuni crystal, which is deadly to creatures of the Shadowlands.
You can forge a weapon out of Kuni crystal, if you meet the other prerequisites for doing so (holy smite or jade strike and daylight). You must first create the weapon, using the rules for the Craft skill in the Player's Handbook (a Kuni crystal weapon adds 400 gp to the listed weapon price and has a DC of 20). Then you must enhance the weapon, which takes one day for each 1,000 gp in the price of its magical features. To enhance a weapon, you must spend 1/25 of its features' total price in XP and use up raw materials costing half this total price. See Chapter 8: Magic Items for details of Kuni crystal weapons' cost and abilities.
Weapons and other items made from normal crystal are not inherently dangerous to Shadowlands creatures, nor do they possess any other extraordinary abilities, unless specifically augmented.