I just now thought of something: Even were humans to find some of this crystal, how could they even dream of destroying Zal-Ghombvis? Even the Dorlyans couldn't do it, and they had these weapons, plus they were like demigods of war!
Appearing a small ballista bolt, this ‘bolt’ is actually an arrow used by a god from a long-dead pantheon. Some sages theorize it was a weapon crafted by Loki to slay the world tree. Why it was never used escapes them however.
The spear has a divine-level anti-plant effect. When driven into the soil point first, a ever widening circle of destruction radiates out from the point, killing any plant material. Perfect for holding a kingdom’s food supply for ransom.
How far it extends depends of course on the GM, of course.