Tulu-metal is a fictional extraterrestrial substance featured in the novella The Mound, written by H. P. Lovecraft based on a story prompt by Zealia Bishop.
Description[]
Tulu-metal (named after the K'n-yanian god "Tulu", a.k.a. Cthulhu) is a heavy, dark, lustrous and "richly mottled" metal that doesn't occur naturally on Earth, but has been brought to the planet by Cthulhu. Objects made of this material are attracted to each other, as if by magnetism, but have no such effect on common magnetic metals. Chemical analysis has identified it as "an amalgam of unknown metallic elements of heavy atomic weight".
The K'n-yanians always had a deep respect for this rare substance, which has grown to a quasi-religious veneration over the course of their history. Objects made of Tulu-metal include "Cyclopean idols" and talismans, as well as metallic cylinders used to store sacred scrolls. The manuscript of Zamacona y Nuñez, who was kept captive in K'n-yan in the 16th century, was found inside one such cylinder.
At one point in history, the currency of K'n-yan was made of Tulu-metal, combined with other elements such as iron, gold, silver, copper, or zinc, so as to greatly diminish its magnetic properties and make it more practical to use.
Since the K'n-yanians have cut off all trade with the surface world after the cataclysms caused by the "space-devils", Tulu-metal is almost unheard of outside K'n-yan.
A talisman made of this metal belongs to the Wichita Chief Grey Eagle, having been passed down from father to son for countless generations of his family. As all of Grey Eagle's ancestors lived for well over a century like him and perished only in battle, it has been speculated that the talisman might be responsible for their longevity, although it's not known whether it is connected to the K'n-yanians' own immortality.
Grey Eagle's talisman is about two inches in diameter and decorated with an image of Cthulhu on one side and Yig on the other, these being the two gods originally worshiped by the K'n-yanians. An identical talisman had previously been found by Zamacona at the entrance of K'n-yan, and worn by him when he first made contact with its inhabitants. Zamacona also found a large sculpture of Cthulhu made of the same metal. (HPL: The Mound)
Behind the Mythos[]
Although Tulu-metal only appears in The Mound, it might be related to the unnamed alien stone of which the idols of Cthulhu are made of in "The Call of Cthulhu". These are also stated to have been brought to Earth from the stars by the Cthulhi, and resemble no kind of mineral known to Earth, being described as soapy and greenish-black with iridescent striations.
Tulu-metal is also similar to the mysterious lagh metal featured in "Out of the Aeons", which is likewise alien to Earth, having been brought from Yuggoth. Like the K'n-yanians, the Muvians use this metal to make cylinders to store important scrolls.