MELNIKOVITE
Class : Sulfides and sulfosalts
Subclass : Sulfides
Crystal system : Cubic
Chemistry : FeS2
Rarity : Uncommon to fairly common
Melnikovite is a colloidal iron sulfide usually classified for convenience among the varieties of pyrite (or sometimes greigite for some authors). But the case of melnikovite is not simple : its nature as a non-crystallized gel makes it, like opal, a body at the limit of the mineral world. Furthermore, as this unstable colloidal gel slowly evolves into marcasite or pyrite, its existence is considered hypothetical, or even false, in Anglo-Saxon mineralogical reference works. It is a supergene variety of pyrite quite common in low temperature hydrothermal veins where it seems to come from the reprecipitation in a reducing environment of iron sulfides. It was named in reference to its discovery location : the Miocene chalk of the state of Melnikov (Russia). The appearance of melnikovite is however characteristic, in zoned concretionary deposits or in yellowish spherules quickly passing to bronze then to reddish. Unlike marcasite, spherulites are never fibrous.
Main photo : Pyrite balls from Cap Blanc-Nez, Pas-de-Calais, France
Melnikovite in the World
Twinning
No twin known for this mineral species.
Fakes and treatments
No fakes recorded for this mineral species.
Hardness : 6 to 6.5
Density : 4.95 to 5.10
Fracture : Irregular to conchoidal
Streak : Black
TP : Opaque
RI : -
Birefringence : -
Optical character : -
Pleochroism : None
Fluorescence : None
Solubility : Nitric acid
Magnetism : NoneRadioactivity : None