Eternal ice

This substance is a rare material found on the Paraelemental Plane of Ice. Also known as unmelting crystal, this ice can withstand any temperature without losing its form. It is often used in the creation of weapons or other various items, though such products are quite rare, both due to the scarcity of this material and the difficulty of working it into any usable shape. Collecting eternal ice is a tricky endeavor, as it's almost indistinguishable from normal ice on the plane; only after further study on the plane or examination outside it can its true nature be determined.

References

• The Inner Planes, pg. 73
• The Planewalker's Handbook, pg. 29