Fletcherite: Properties and Occurrences

Fletcherite is a rare thiospinel sulfide mineral with formula Cu(Ni, Co)2S4. It is an isometric-hexoctahedral steel-gray mineral containing cobalt, copper, nickel, and sulfur. It is an opaque metallic steel-gray mineral which crystallizes in the cubic crystal system. It is a member of the linnaeite group.

It was first described in 1977 as an occurrence in the Fletcher Mine, Viburnum Trend (New Lead Belt), near Centerville, Reynolds County, Missouri.

General Information

  • Category: Sulfide mineral (Thiospinel group)
  • Formula: Cu(Ni, Co)2S4
  • Crystal system: Cubic
  • Crystal class: Hexoctahedral (m3m)

Fig: Fletcherite –┬áthiospinel sulfide mineral

Properties

  • Color: Steel gray, creamy white in polished section
  • Crystal habit: Minute subhedral to euhedral crystals typically enclosed within other sulfide minerals
  • Mohs scale hardness: 5
  • Luster: Metallic
  • Diaphaneity: Opaque
  • Specific gravity: 4.76 calculated
  • Polish luster: Good polish with moderate reflectivity
  • Optical properties: Isotropic

Occurrence

Disseminated in copper sulfides, in copper-rich pods replacing dolostone (Fletcher mine, Missouri, USA); in black slates (Kalgoorlie, Australia). It occurs as dissemination within copper sulfide minerals in mineralization replacing dolostone at the type locality in the Fletcher mine where it is associated with vaesite, pyrite, covellite, chalcopyrite, bornite, and digenite. In an occurrence in Kalgoorlie, Australia it is found in black slate associated with pyrrhotite.

Association: Vaesite, pyrite, covellite, chalcopyrite, bornite, digenite (Fletcher mine, Missouri, USA); pyrrhotite (Kalgoorlie, Australia).

 

Information Source: