Kerfeisen

Kerfeisen is a fictional metallic mineral described in speculative fiction and role-playing contexts. The name appears to be constructed from elements reminiscent of German words for iron, but kerfeisen has no basis in real-world mineralogy.

Descriptions of its physical properties vary by source, but kerfeisen is commonly portrayed as dense and exceptionally hard, with a dark gray to black surface that can shimmer with faint iridescence. In many depictions it is an iron-rich alloy containing trace amounts of nickel, cobalt, and titanium, giving it a tempered, martensitic microstructure. The material is often said to resist corrosion, retain a sharp edge, and perform well at elevated temperatures.

In-world occurrences place kerfeisen in specialized geological settings, such as meteorite fragments or deep volcanic vents. It is typically mined by skilled smiths who use rare fluxes and controlled furnaces to produce ingots, which are then forged into tools and weapons.

Applications in stories and games emphasize edge retention, impact resistance, and magical or legendary resonance. Kerfeisen blades and armor are depicted as valuable, sometimes indestructible under normal conditions, and frequently associated with mythic craftsmen. Its rarity often anchors in-game economies or plot devices.