"Rock of the Month # 5, posted November 2001" --- Sample 2261.

Violarite, a violet-grey sulphide of iron and nickel, ideal formula FeNi₂S₄ (38.93 weight percent Ni), is a moderately uncommon cubic ore mineral, found in some nickel deposits. This sample is from the Vermilion mine west of Sudbury, Ontario*. Seen in photomicrograph with yellow millerite (NiS). The violarite has a characteristic grey colour with a violet tint, and displays cubic cleavage traces. Magnification 80X, long-axis field-of-view 1.4 mm, plane-polarized, reflected light.

The ore also contains patches of coarse pyrite with ragged inclusions of chalcopyrite. The hand specimen, which is not appreciably magnetic, contains roughly 90 volume percent massive sulphides plus 10 percent silicate inclusions. This sample was obtained from Gil Benoit. The polished thin section contains an estimated 70 volume percent violarite plus 15% intimately associated millerite, with patches of coarse pyrite (7%) and associated chalcopyrite (1%), and 7% gangue minerals (quartz, biotite mica and carbonate). The surface is heavily rusted, with local iridescent green tarnish, and the sawn surface contains what appear to be small amphibole prisms.

Violarite appears often in early supergene modification of nickel ores (Arnold and Malik, 1974), where pentlandite and pyrrhotite may be respectively replaced by violarite and marcasite. Violarite may also replace the Ni-rich millerite. It occurs in a range of Ni-rich deposits around the world, in Western Australia, New Zealand, South Africa, Orissa (India), Saudi Arabia, Ontario and Quebec, Manitoba and Saskatchewan, British Columbia and Yukon, and elsewhere. Violarite is a member of the linnaeite group of sulphides: the photograph displays the combination of distinct cleavage and poor polishing noted in this group (Riley, 1980).

The Vermilion mine has received less academic attention than some of the better-known mines in the district. It is however known for the occurrence of platinum- group minerals and other unusual species (Wells, 1889; Cabri, 1972; Gait and Harris, 1972, 1980; Grice and Ferguson, 1989)*. The Vermilion mine is noted as the type locality of violarite, and of the rare mineral arsenohauchecornite, Ni₁₈Bi₃AsS₁₆, a bronzy tetragonal phase first described at this mine by Gait and Harris (1980). It is also remembered as the source of many specimens of "coarse-grained" (i.e., >1 mm) crystals of the steely-grey platinum arsenide, sperrylite.

* Footnote on place names

References

ARNOLD,RG and MALIK,OP (1974) Violarite in some nickel ores from Lynn Lake and Thompson, Manitoba, and Sudbury, Ontario, Canada. Can.Mineral. 12, 320-326.

CABRI,LJ (1972) The mineralogy of the platinum-group elements. Min.Sci.Eng. 4 no.3, 3-29.

GAIT,RI and HARRIS,DC (1972) Hauchecornite from the Vermilion mine, Sudbury district, Ontario. Can.Mineral. 11, 573.

GAIT,RI and HARRIS,DC (1980) Arsenohauchecornite and tellurohauchecornite: new minerals in the hauchecornite group. Mineral.Mag. 43, 877-878.

GRICE,JD and FERGUSON,RB (1989) The crystal structure of arsenohauchecornite. Can.Mineral. 27, 137-142.

RILEY,JF (1980) Ferroan carrollites, cobaltian violarites, and other members of the linnaeite group: (Co,Ni,Fe,Cu)₃S₄. Mineral.Mag. 43, 733-739.

WELLS,HL (1889) Sperrylite, a new mineral. Amer.J.Sci. 137, 67-70.