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Category Sulfide mineral
(repeating unit)
Strunz classification 2.EB.05a
Crystal system Cubic
Crystal class Diploidal (m3)
H-M symbol: (2/m 3)
Space group Pa3
Unit cell a = 5.58 Å: Z = 1
Color Dark brownish gray; pinkish brown in polished section
Crystal habit As intergrowths with pyrite and covellite, grains less than 1 μm
Mohs scale hardness 4 - 6
Luster Submetallic
Diaphaneity Opaque
Specific gravity 4.86
Optical properties Isotropic
References [1][2][3]

Fukuchilite, Cu3FeS8, is a copper iron sulfide named after the Japanese mineralogist Nobuyo Fukuchi (1877–1934), that occurs in ore bodies of gypsum-anhydrite at the intersection points of small masses of barite, covellite, gypsum and pyrite, and is mostly found in the Hanawa mine in the Akita prefecture of Honshū, Japan where it was first discovered in 1969. It occurs in masses within the third geologic unit of the Kuroko type deposits within the mine.

As a copper, iron sulfide, it is placed in the same group as bornite and chalcopyrite, and most fukuchilite locations are found in relatively close proximity to these minerals. Fukuchilite was found to have a reflection color very similar to bornite and bright pinkish brown in air, while being a purplish brown in oil. Also, it was found to have a reactivity lower than pyrite, but distinctly higher than bornite.[4] It has a Mohs hardness of 4-6, a specific gravity of 4.9, and a sub metallic luster, composed of 11.1% iron, 37.9% copper, and 51.00% of sulfur.[5]

It is in the isotropic cubic crystal system with symmetry: (2/m3), space group P a3. Much relating to the structure of the mineral is still under debate, and some believe that fukuchilite might actually be a form of villamaninite (Cu,Ni,Co,Fe)S2,[6] but fukuchilite currently still holds its mineral status as there is currently not enough evidence to discredit an already accepted and titled mineral.[5]


  1. ^ Fukuchilite on Mindat.org
  2. ^ Fukuchilite in the Handbook of Mineralogy
  3. ^ Fukuchilite data on Webmineral
  4. ^ Kajiwara, Yoshimichi. "Fukuchilite, Cu3FeS8, a New Mineral From the Hanawa Mine, Akita Prefecture, Japan." Mineralogical Journal 5 (1969): 400-415.
  5. ^ a b Bayliss, Peter. "Crystal Chemistry of Some Minerals Within the Pyrite Group." American Mineralogist 74 (1989): 1168-1176
  6. ^ Villamaninite Mineral Data
  • Terakado, Yasutaka, and Richard J. Walker. "Nd, Sr and Pb Isotopic and REE Geochemical Study of Some Miocene Submarine Hydrothermal Deposits (Kuroko Deposits) in Japan." Contributions to Mineralogy and Petrology 149 (2005): 388-399