Rhodium, Rh, is quite a rare member of the platinum-group of metals with an average crustal value of 0.2 ppb. Most economic rhodium comes from as a by-product of certain copper-nickel ores. The world's major producers are South Africa, Russia and Canada. Annual production stands at a...

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round 30 tonnes per year. The most important industrial uses are in automobile catalytic converters, optical fibres, chemical industry, optical mirrors, thermocouples, headlight reflectors, laboratory crucibles, coatings for electrical contacts and measuring neutron fluxes in nuclear reactors. Most of its minerals are found in the sulphide or elements class.


Rhodium, Rh, is a uncommon cubic mineral from heavy mineral concentrates and is associated with many platinumgroup minerals such as platinum, moncheite, kotulskite, merenskyite, cooperite, braggite, vysotskite, sperrylite, and gold, pyrite, chalcopyrite, pyrrhotite, chromite, magnetite, marcasite, violarite and graphite.

It occurs as tiny metallic grains with a silver-white colour and is opaque. Its hardness is 3.5 and the specific gravity is high at 16.5. Chemistry, mode of occurrence and x-rays are best for identification. The mineral has been reported from only a few places such as, the Stillwater Complex, Montana, and at Fox Gulch, Alaska, USA: the Kleva mine, Vetlanda, Sweden; Maandagshoek farm, Bushveld Complex, South Africa; the Sukhoi Log deposit, Lena Gold district, Siberia, Russia; the Luobusha ophilite, Shannan Prefecture, China; and at the Wilson River mineral field, Tasmania, Australia.

Hollingworthite, (Rh,Pt,Pd)AsS, forms small tabular to pseudohexagonal crystals.
Small anhedral grains are also known to occur. It is iron-black in colour with a metallic lustre. Its hardness is greater than 6. The specific gravity varies from 7.2 to 7.8.
Chemistry and x-rays are most suitable techniques for characterisation.

This mineral occurs in layered ultramafic intrusions, dunites and in concentrates accompanied by sperrylite, geversite, erlichmanite, irarsite, chalcopyrite, cobaltite, gerdsorffite, pyrrhotite, braggite, pentlandite, and pyrite. Hollingsworthite is known from a variety of scattered locations worldwide and includes those in South Africa, Zimbabwe, Finland, Austria, Serbia, USA, Canada, Russia, Scotland, Norway and Australia.

Cherepanovite, RhAs, is an orthorhombic mineral that forms small grains and aggregates with one distinct cleavage. The mineral is black in colour with a greyish black streak and is metallic. The hardness is 6. The specific gravity is 9.7.

It is a late stage mineral of platinum-group mineral assemblages of ultramafic rocks and some placers with isoferroplatinum, tetraferroplatinum, rutheniridosmine, laurite, irarsite, cooperite, sperrylite, hollingsworthite, chromite and other species. X-rays and chemical tests are best.
This uncommon mineral occurs in sites in Russia, South Africa, USA and New Zealand.

Bowieite, (Rh,Ir,Pt)2S3, is a mineral of platinum-alloy nuggets and from weathered ultramafic rocks with platinum, iridium, osmium, laurite, cooperite, kashinite, cuprorhodsite and other minerals. It is found as anhedral grains and crystallises in the orthorhombic system.

The mineral is pale grey to pale grey-brown colour in reflected light. The mineral is metallic and is slightly brittle in character.
The hardness is high at 7 with a specific gravity of 6.9. Chemistry and x-rays are useful for identification. This rare species occurs in some deposits in USA, Ethiopia, Burma, Russia, Colombia, Ecuador, China and Madagascar.

Cuprorhodsite, CuRh2S4, is a cubic species that is found as small isometric grains that are round or irregular from alluvial placers.
It is associated with isoferroplatinum, cuproiridsite, malanite, osmium, iridosmine, laurite, erlichmanite, cooperite, sperrylite, chacopyrite and bornite. The mineral is iron-black in colour with a metallic lustre. It is very brittle with a hardness of 5-5.5. Chemistry and x-ray methods are best here.

Several reported occurrences for this uncommon species are known: These are mainly in Russia, but also in Italy, Spain, France, Finland, Austria, Brazil, Canada, Columbia, Ecuador, Ethiopia, Madagascar, and in New Caledonia.

Konderite, PbCu3(Rh,Ir,Pd,Co,Pt)8S16,complex hexagonal sulphide which occurs as irregular inclusions on very thin orientated laths of erlichmanite in Pt-Fe alloys. Other accompanied species are cuproiridsite, kashinite, sperrylite, cooperite and other alloys.

It is steel-grey in colour with a metallic lustre and is opaque. Its hardness is 5.5, and it is brittle. It possesses distinct and good cleavages. The calculated specific gravity is high at 10.2. X-ray and chemical methods are used to identify it. Konderite is has been discovered in three countries: In Finland at the Kirakkajuppura PGE deposit, Penikat complex; the Konder mine, Aldan shield, Ayan-Maya district, Russia; and at Goodnews Bay, Alaska, USA.

Ferrorhodsite, (Fe,Cu)(Rh,Pt,Ir)2S4, occurs in dunite as inclusions (irregular and equant grains) in isoferroplatinum with laurite, osmium and hollingworthite. It is a cubic mineral that is black in colour with a black streak. The lustre is metallic and is
opaque with hardness of 4.5. Its calculated specific gravity is 5.7. Chemistry and x-rays are suitable for certain characterisation.

Five locations are known for this scarce mineral: They are Kraubath, Styria, Austria; Bir Bir River, Gimbi, Ethiopia; Kirakkajuppura PGE deposit, Penikat complex, Finland; and in two localities in Russia i.e. Mount Filipp, Kamchatka Oblast and the Chad massif area.

Rhodplumsite, Pb2Rh3S2, is a grey metallic mineral that crystallises in the trigonal system. Other properties are unknown but its calculated specific gravity is around 10.0.

It occurs as small grains associated with platinum, osmium, iridium and laurite, Xray and chemical methods are used for correct identification of this scarce mineral.
The single locality for the species is the Omutninskaya placer deposit, Omutnaya River, Sysert District, Russia.

 

by john betterton

The next article will deal with the rarer members of the PGM, namely iridium, osmium and ruthenium.

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