[MSA-talk] Mineral name for perovskite-structured (Mg, Fe) silicate?

Robert Tracy rtracy at vt.edu
Tue May 27 15:49:02 EDT 2014


Anachronism it may be in your opinion (and the IMA's) but I will resolutely continue to use the name Sphene whenever I am allowed to get away with it. The IMA has done some stupid things over the years (magnesian ferrosilite anyone?) but the outlawing of the beautiful (and unambiguous) name Sphene is top of my list.

Dr. Robert J. Tracy
Prof. of Geosciences
Associate Department Head
Director, Museum of Geosciences
Virginia Tech
Blacksburg VA 24061-0420
540-231-5980
540-231-3386 (F)




On May 27, 2014, at 11:28 AM, Anton Chakhmouradian wrote:

> For all purposes, MgO with subordinate Fe in the lower mantle IS periclase (its rock-salt structure is very robust and persists to > 200 GPa; Duffy et al., Phys. Rev. Let., 74, 1371). At ambient conditions, FeO is isostructural with periclase and known as the mineral wüstite (in addition to metallurgical slags, it occurs in meteorites and a few obscure terrestrial environments). The intermediate Mg-dominant members should then be termed Fe2+-rich (-bearing) periclase, according to the IMA guidelines. The rock-salt structure of FeO transforms into a rhombohedral polymorph at 18 GPa, but the presence of Mg seems to stabilize the rock-salt arrangement throughout the lower-mantle P range (see, e.g., Lin et al., PNAS, 100, 4405). That means that, from the standpoint of nomenclature, we are dealing with compressed intermediate members of the periclase-wüstite series. Any other name applied in the literature (magnesiowüstite, ferropericlase, ferroan periclase, etc.) is not in accord with the IMA recommendations. Of course, people still use this “illegal” terminology, just like one can still bump into sphene, melanite, picroilmenite and numerous other anachronisms in the Min-Pet literature.
>  
> Anton Chakhmouradian
> University of Manitoba
>  
>  
> From: msa-talk-bounces at minlists.org [mailto:msa-talk-bounces at minlists.org] On Behalf Of Charles Carrigan
> Sent: Tuesday, May 27, 2014 9:56 AM
> To: David Hirsch; MSA-talk (msa-talk at minlists.org)
> Subject: Re: [MSA-talk] Mineral name for perovskite-structured (Mg, Fe) silicate?
>  
> How about MgO with rock-salt structure referred to as “magnesiowustite”?  I’ve even seen a reference to FeO as “ferropericlase”. 
>  
>  
> Best,
> Charles
>  
> <image003.png>Charles W. Carrigan, Ph.D.
> Professor of Geoscience │ Dept. of Chemistry & Geosciences
> Director, University Honors Program
> Olivet Nazarene University │ One University Avenue │ Bourbonnais, IL 60914
> Office: 815.939.5346 │ web │ email │ Honors: 815.928.5613 │ Fax: 815.939.5071
>  
>  
> From: msa-talk-bounces at minlists.org [mailto:msa-talk-bounces at minlists.org] On Behalf Of David Hirsch
> Sent: Tuesday, May 27, 2014 9:31 AM
> To: MSA public List serve
> Subject: [MSA-talk] Mineral name for perovskite-structured (Mg, Fe) silicate?
>  
> Friends-
> I’ve just read a news release online about the new Zhang, et al. Science paper "Disproportionation of (Mg,Fe)SiO3 perovskite in Earth’s deep lower mantle”.  Is there a mineral name for the perovskite-structured (Mg,Fe)SiO3 mineral?  If not, then shouldn’t we come up with one?  It seems to me that the name “perovskite” should apply to the CaTiO3 mineral, and that it’s wrong to apply it to the isostructural silicate, just as we don’t give the same mineral name to halite and galena.  The article title isn’t so bad, but when you get news releases that include this kind of thing, then there’s a real problem:
>  
> "The prevailing theory has been that the majority of the lower mantle is made up of a single ferromagnesian silicate mineral, commonly called perovskite (Mg,Fe)SiO3) defined through its chemistry and structure. It was thought that perovskite didn't change structure over the enormous range of pressures and temperatures spanning the lower mantle”
>  
> The release’s author here has presumably misinterpreted the article’s title to infer that “perovskite" is the name of the mantle mineral, rather than "(Mg,Fe)SiO3 perovskite”, indicating a perovskite-structured silicate.
>  
> I understand that an official mineral name is not possible, since it cannot be found occurring naturally and fully described, but perhaps if the community decided on a name we could use in lieu of the (to me) troubling "(Mg,Fe)SiO3 perovskite” or worse “perovskite”, then there might be a little more clarity and a little less confusion out there, at least among mineralogy students.
> -Dave
>  
> ============================
> Dave Hirsch
> Associate Professor
> Department of Geology
> Western Washington University
> alternate email: dhirsch at mac.com
> http://www.davehirsch.com
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