Reassessment of the Volkonskoite-Chromian Smectite Nomenclature Problem

Abstract

Abstract--The name volkonskoite was first used in 1830 to describe a bright blue-green, chromiumhearing clay material from the Okhansk region, west of the Ural Mountains, U.S.S.R. Since that time, the name has been applied to numerous members of the smectite group of clay minerals, although the reported chromium content has ranged from 1% to about 30% Cr203. The name has also been applied to some chromian chlorites. Because volkonskoite has been used for materials that differ not only in their chromium content but also in their basic structure, the species status of the mineral has been unclear.To resolve this uncertainty, two specimens of volkonskoite from (1) Mount Efimiatsk, the type locality in the Soviet Union (USNM 16308) and (2) M6ssbauer spectroscopy indicates that 91% and 98% of the iron is present as Fe 3+ in samples 16308 and R4820, respectively. X-ray powder diffraction patterns of both samples have broad lines corresponding to minerals of the smectite group.On the basis of these data, volkonskoite appears to be a dioctahedral member of the smectite group that contains chromium as the dominant cation in the octahedral layer. Smectites containing less than this amount ofoctahedral chromium should not be called volkonskoite, but should be named by chemical element adjectives, e.g., chromian montmorillonite, chromian nontronite.

Reassessment of the Volkonskoite-Chromian Smectite Nomenclature Problem: Comment

“…Their suggested solution--namely, the definition of volkonskoite as a dioctahedral member of the smectite group containing dominant chromium in the octahedral position-however, leaves, as so often happens, another problem--the most suitable name for the mineral from Jordan described by Khoury et al (1984). In their paper, Foord et al (1987) recommended that the Jordanian mineral be termed 'chromian montmorillonire', a name that seems somewhat inappropriate in view of the fact that this mineral contains only Cr 3+ and Mg 2+, but no A13+, in the octahedral sheet. Although Mg slightly exceeds Cr, 'chromian saponite' is unsuitable, as the mineral is dioctahedral despite YY~ being greater than 4--as it seems to be in all high-chromian smectites.…”

“…Moreover, the name 'chromian smectite' is particularly nondescript for such a well-characterized and homogeneous mineral, and the only possibility left seems to be the introduction of a new name. This problem could have been solved without raising further difficulties had Foord et al (1987) phrased their definition: 'A dioctahedral member of the smectite group containing chromium as the dominant trivalent cation in the octahedral sheet'--a definition that I understand was adopted by the Nomenclature Committee of Association Internationale pour l'Etude des Argiles at Denver in 1985 (S. W. Bailey, University of Wisconsin, Madison, Wisconsin, 1988, private communication). Perhaps it is not yet too late to make this alteration.…”

Reassessment of the Volkonskoite-Chromian Smectite Nomenclature Problem: Reply

“…A simple definition of the mineral species volkonskoite was given by Foord et al (1987) and approved by the International Mineralogical Association Commission on New Minerals and Mineral Names (IMA) (E. H. Nickel, Division of Mineralogy and Geochemistry, CSIRO, Wembly, Western Australia, Australia, written communication, 1985) as "a dioctahedral member of the smectite group having Cr as the dominant octahedral cation". Mackenzie ( 1988), however, has pointed out that the definition of volkonskoite should be further restricted by defining this species as "a dioctahedral mineral of the smectite group containing chromium as the dominant trivalent (emphasis added) cation in the octahedral sheet", a definition approved by the Nomenclature Committee of the Association Internationale pour l'Etude des Argiles (AI-PEA) (see supplement to AIPEA Newsletter No.…”

“…22, February 1986). Newman and Brown (1987) defined volkonskoite in the same manner as Foord et aL (1987).…”

“…The mineral is apparently dioctahedral, but has some trioctahedral characteristics. If, on the other hand, the definition approved by IMA and used by Foord et aL (1987) and Newman and Brown (1987) is applied, this mineral should be given a new name.…”