Black metallic crystals of the very rare Cu-Pb-Bi sulphosalt mineral nuffieldite from USA (Granite Gap, Hidalgo County, New Mexico, United States of America), associated to a green mineral that it is probably malachite. — Photo: David Hospital · CC BY-SA 4.0
Nuffieldite
Nuffieldite is an IMA-recognized mineral species in the sulfosalt class, with the chemical formula Cu₁.₄Pb₂.₄Bi₂.₄Sb₀.₂S₇.
It crystallizes in the orthorhombic crystal system (space group Pbmn). It is a member of the Kobellite structural group.
Key properties: specific gravity 7.01; Dark greenish gray to black streak; Bright metallic. Anisotropism: Very weak, from bluish gray to grayish red. R1 –R2: (400) 35.9–45.5, (420) 36.7–44.6 luster.
IMA symbol Nuf, IMA status: approved, named in 1967.
Found in vugs in a small quartz vein in the Lime Creek stock (Lime Creek deposit, Canada).
It is found associated with Molybdenite, cosalite, aikinite, pyrite, galena, sphalerite (Lime Creek, Canada); neyite, galena, tetrahedrite, chalcopyrite, sphalerite (Alaska mine.
In honor of Professor Edward Wilfrid Nuffield (1914–), Canadian mineralogist of the University of Toronto, Toronto, Canada.