Töölei

Töölei is a metasematite mineral species that was first described in 1946. It is primarily found in nickel-copper deposits and is known to occur in a range of geological settings, including igneous and sedimentary rocks. Töölei crystals can be found in association with other minerals such as pyrrhotite, pentlandite, and chalcopyrite.

Töölei is named after the Estonian word for "work ore," which refers to its occurrence in mines. The mineral has a strong sulfur smell and is typically found in an assemblage with other sulfide minerals. Töölei is a moderately hard mineral with a Mohs hardness of approximately 4-5.

Chemically, töölei is composed of a nickel-iron-sulfur alloy with the chemical formula NaFe3S5, although it has also been reported to occur in a copper-iron-sulfur crystal structure with the formula Cu3FeS5. The mineral has a primarily black or dark brown color and displays a metallic luster. Töölei often has a striated or curved habit and can form aggregates or grow in tabular crystals.

The occurrence of töölei is primarily limited to a few specific localities, including the Estonian nickel-copper deposits and the Koillismaa ore field in Finland. It is not commonly found in museums or collections due to its rarity, but samples can be found in the collections of geological institutions and research centers. In summary, töölei is a distinct and relatively rare mineral species that has been of interest to geologists and mineralogists due to its unique composition and occurrences in nickel-copper deposits.