THE MINERAL
RAMMELSBERGITE


  • Chemistry: NiAs2, Nickel Arsenide.
  • Class: Sulfides
  • Subclass: Arsenides
  • Group: Marcasite and Lollingite
  • Uses: As a very minor ore of nickel and arsenic and as mineral specimens.
  • Specimens
Rammelsbergite is a difficult mineral to distinguish from other nickel sulfides and related arsenides. Its unusually high hardness and silvery color helps, but mostly it is indistinguishable from many of them by ordinary methods. It had been reported to have been found at Franklin, New Jersey, but this may have been a misidentification with the mineral gersdorffite, a similar looking nickel arsenic sulfide.

Rammelsbergite is a rare mineral, but is found with other arsenides and thus it is included with them when mined for nickel and/or arsenic. It is a member of the Lollingite Group. The namesake of the group, lollingite is closely related, but has more iron than nickel in its chemistry. Another closely related mineral is saffloriite, which has more cobalt than nickel. The three minerals share the same basic structure and just differ by chemistry. The lollingite group is sometimes placed in the larger Marcasite Group.

Rammelsbergite lends it name to its dimorphic cousin, pararammelsbergite. A dimorph is a set of two minerals that share the same chemistry, but have different structures. Pararammelsbergite has monoclinic symmetry, while rammelsbergite's is orthorhombic, (the prefix para just means "similar to...").

PHYSICAL CHARACTERISTICS:

  • Color is silvery white, almost reddish (tarnishes to yellow or pink).
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include rare tabular to stubby crystals, sometimes in cock's comb habit. More commonly found fibrous (radially), massive and granular.
  • Cleavage is absent.
  • Fracture: Uneven.
  • Hardness is 5.5 - 6
  • Specific Gravity is approximately 6.9 - 7.1 (well above average for metallic minerals)
  • Streak is a gray.
  • Associated Minerals include niccolite, gersdorffite, quartz, annabergite, pyrite, lollingite, chloanthite, arsenic, cobaltite, arsenopyrite and silver.
  • Notable Occurrences include the Sainte-Marie-Aux-Mines district, France; Great Bear Lake and the Frontier Mine, Cobalt, Ontario, Canada; Kongsberg, Norway; Binntal Switzerland; Lolling, Austria; Bou Azzer, Morocco; Batopilas, Chihuahua, Mexico; Keweenaw, Michigan and the type locality of Schneeburg, Harz Mountains, Germany.
  • Best Field Indicators are crystal habits, color (tarnish), associations, streak, hardness and density.
RAMMELSBERGITE specimens:
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RAMMELSBERGITE specimen rml-1
$ 32.00
Dims: 1.2x0.6x0.6" (3.0x1.5x1.5cm)
Wt: 0.57 oz. (16.2g)
Schneckenstein, Sachsen, Germany
This is an excellent thumbnail specimen of rammelsbergite, considering that there are no distinct crystals. The form is massive, and the color is an excellent silvery-white. One face of the specimen has a very unusual radial pattern of narrow columns with basal striations. My first impression was that it looked like a fossil shell, however the pattern extends into the specimen so it must result from mineral growth. There are other minerals present, red and transparent on one side, black, sparkly and transparent on the other, and some colorless mineral. All of these might be variously colored calcite, or something else entirely. I could not find good crystals to examine.
no photo
rml-1 ($ 32.00)
Schneckenstein, Sachsen, Germany
 

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