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Krystaalc is a neon yellow/green colored glowing crystal that is found in one massive collection on the roof of The Depth, almost like the sun, but underground. These crystals are very brittle and will commonly break off of the main deposit and attach to the floor of The Depth’s underground ocean to form secondary deposits. Either that or drift through said ocean endlessly. Additionally, it’s immune to exploding because of contact with The Fiery Shell.
But perhaps the greatest use of Krystaalc is it’s ability to fuse. Krystaalc can be fused by simply bashing it against a solid surface. It’s chemical composition makes it impossible to squeeze together, but trivial to fuse, and that’s why it’s easy. The main use of fusing it however is to create Krystaalc-B, because when regular Krystaalc and Krystaalc-B touch(which is pretty much always because Krystaalc-Bis made from regular Krystaalc, an endothermic reaction occurs, cooling the surrounding area. This is very useful in Broadbarrel, being used as primitive air-conditioners, to even increasing the density of air in submarine-like vehicles so that they descend into the water.
Weaponry and ammunition can be studded with Krystaalc to make it more effective. You can stud a single weapon or ten pieces of Ammunition for 100 gp. This cost represents not only the price of the Krystaalc, but the time and expertise needed to stud the weapon with Krystaalc without making it less effective. A studded weapon deals cold damage if the opponent has resistance or immunity to whatever type of damage it normally is unless the opponent also has resistance or immunity to cold damage. It will also deal cold damage if the creature is vulnerable to cold damage. For example, the players are fighting an astral dreadnought. Say a party member is attacking with a Krystaalk studded mace. Normally, since it is nonmagical, the astral dreadnought would have resistance to the attack, but because it is studded with krustaalc, instead, it deals cold damage, and the astral dreadnought takes full damage instead of half.