Prassoite

Prassoite: the mineral prassoite, Rh₃S₄, was approved as mineral 70-041 by the CNMMN in March 1971. The author, Kingston, published some data in his Ph.D. thesis in 1977. These data were summarized by Cabri in 1981, but he stated that the true formula might be Rh₁₇S₁₅ (Mandarino, J.A. & M.E. Back (2004), Fleischer's Glossary of Mineral Species: 219).

Augé found the same mineral as Kingston in 1988, with the formula Rh₃S₄ (Can. Mineral. 26, 177-192), and this paper was mentioned by Jambor in 1989 (Am. Mineral. 74, 1220).

Britvin et al. proposed the mineral Miassite (97-029) to the CNMMN with the formula Rh₁₇S₁₅. This mineral was approved in October 1997, but the name was suspended because of possible problems with prassoite. The authors were asked to contact Kingston. They tried to do so, but to no avail.

After having heard from Britvin et al. that Kingston did not reply to any search, the suspension on the name miassite was lifted, but the CNMMN chairman then made a mistake (probably by not having access to the 1971 archives).

In his Memorandum of July 1999, Joel Grice wrote: 'Prassoite' was never approved by the CNMMN, and no type material can be found. It is apparent that the authors of miassite have done everything possible to establish or
refute the existence of this dubious mineral and the name 'prassoite' is to be discouraged from further usage. In his letter to Britvin et al., lifting the suspension, Joel Grice wrote: I would ask you to make it clear in your publication that all attempts were made to find the type material for a formal discrediation of prassoite but none existed.

Britvin ,et al. published their Miassite in ZVMO 130(2), 41-44 (2001), stating in the paper that prassoite was never approved by the CNMMN, this of course on the authority of Joel Grice. The paper was abstracted by Jambor (Am. Mineral. 87, p. 1511), with the correction that prassoite had indeed been approved by the CNMMN back in 1971.

Later, it became apparent that the type material of prassoite was present in the British Museum (on the same specimen as the type material for kingstonite), but the letters of Britvin et al. to Kingston were never forwarded to the curator of the British Museum.

We have meanwhile the strange fact that there are at least ten papers using the name prassoite (the most recent one in Can. Mineral. 40 (2002), 1127-1146), but only a single paper on miassite!

Moreover, the name 'prassoite' has never been officially discredited or withdrawn.

In view of the delay in the (incomplete) publication of the inadequately described prassoite and the uncertainties about its composition, the name ‘prassoite’ is withdrawn for the time being in favour of miassite.

Unambigous evidence for the existence of Rh3S4 as a mineral might reinstate the name prassoite.

Re-examination of analyses of the type material indicate that 'prassoite' is actually Ferrorhodsite or Cuprorhodsite (Cabri, pers. comm., reported in Mineralogical Magazine, August 2005, Vol. 69(4), p. 447)