Vesuvianite From Pajsberg, Sweden, and the Role of Be In the Vesuvianite Structure

Abstract

Vesuvianite from Pajsberg, Sweden contains about one atom of Mn, based on 50 cations per formula unit, and small amounts of Be, B, and As. Optical absorption analysis suggests that the Mn is predominantly or entirely trivalent. Crystalstructure analysis indicates that Mn is housed at the general octahedral site Y3, which exhibits only minor distortion from ideal octahedral symmetry. Arsenic is housed at Y2 and Z2, and the formula derived from electron microprobe and LA-ICP-MS analyses suggests minor substitution of Al for Si, also at Z2. Beryllium and B are at T1, between the edge-sharing trimers Y3Y2Y3, as is the case for B in the boron-dominant vesuvianite species wiluite. The total content at T1 is interpreted as 0.82Be, 0.34B, and 0.037Fe 3þ .

Towards a revisitation of vesuvianite-group nomenclature: the crystal structure of Ti-rich vesuvianite from Alchuri, Shigar Valley

“…The Y1 site is coordinated by four O atoms at the O3 site and an apical anion (OH, O or F) at the O10 site forming a square pyramid. In vesuvianite-group minerals this fivefoldcoordinated site can be half-occupied by Mn 2+ , Fe 2+ , Mn 2+ , Fe 3+ , Cu 2+ , Mg 2+ (Ohkawa et al, 1992;Armbruster et al, 2002;Giuseppetti & Mazzi, 1983;Groat et al, 1998;Britvin et al, 2003;Panikorovskii et al, 2015;Fitzgerald et al, 1986). Fivefold (semi-octahedral) coordination of Ti is known in a number of minerals including members of the lamprophyllite group and related heterophyllosilicate schü llerite Rastsvetaeva et al, , 2016, fresnoite (Moore & Louisnathan, 1967) and paranatisite (Sokolova & Hawthorne, 2002).…”

“…Three new vesuvianite-group minerals (manganvesuvianite, cyprine and magnesiovesuvianite) have been approved by the IMA CNMNC during the last 15 years. However, the Al-dominant (at the [5] Y1 site) vesuvianite-group mineral (Fitzgerald et al, 1986) does not have its own name, and the role of Fe valency in Fe-dominant samples is not clarified. The name 'manganvesuvianite' is ambiguous because it can refer to Linear trimer from Y2 and Y3 octahedra in the structure of Ti-rich vesuvianite.…”

“…The vesuvianite group of minerals consists of vesuvianite Ca 19 (Fe 3+ ,Fe 2+ )(Al,Mg,Fe 3+ ) 12 (SiO 4 ) 10 (Si 2 O 7 ) 4 (OH,O) 10 (space group: P4/n; Giuseppetti & Mazzi, 1983), wiluite Ca 19 (Al,Mg) 13 (B, &, Al) 5 (SiO 4 ) 10 (Si 2 O 7 ) 4 (O,OH) 10 (space group: P4/nnc; Groat et al, 1998), fluorvesuvianite Ca 19 Fe 2+ (Al,Mg) 12 (SiO 4 ) 10 (Si 2 O 7 ) 4 (F,OH,O) 10 (space group: P4/nnc; Britvin et al, 2003), manganvesuvianite Ca 19 Mn 3+ Al 10 Mg 2 (SiO 4 ) 10 (Si 2 O 7 ) 4 (OH) 9 O (space group: P4/n; Armbruster et al, 2002), cyprine Ca 19 Cu 2+ (Al 10 Mg 2 )-(SiO 4 ) 10 (Si 2 O 7 ) 4 (OH) 10 (space group: P4/n; Panikorovskii et al, 2015) and magnesiovesuvianite Ca 19 Mg(Al 10 Mg 2 )-(SiO 4 ) 10 (Si 2 O 7 ) 4 (OH) 10 (space group: P4/n; Panikorovskii, Shilovskikh et al, 2016). The crystal structure of a vesuvianitegroup mineral with Al as a predominant cation at the site with fivefold coordination is described by Fitzgerald et al (1986). Vesuvianite varieties containing substantial amounts of rare earth elements (REE; up to 14.74 wt% Ln 2 O 3 : Groat et al, 1992a) and Cr (up to 1.89 wt% Cr 2 O 3 : Hå lenius, 2000) are also known.…”

Vesuvianite from the Somma-Vesuvius Complex: New Data and Revised Formula

“…The tentative vesuvianite formula, (Ca,Na) 19 10 , does not specify the occupancies of the Y1(A,B) site [36], which are responsible for the observed species diversity of the vesuvianite-group minerals [16,21,29]. According to the IMA CNMNC guidelines for compositional criteria [37], at least one structural site in the potential new mineral should be predominantly occupied by a different chemical component than that which occurs in the equivalent site in an existing mineral species [16].…”

“…However, the general formula of vesuvianite given in the International Mineralogical Association (IMA) List of Minerals (http://ima-cnmnc.nrm.se/imalist.htm), (Ca,Na) 19 (Al,Mg,Fe) 13 (SiO 4 ) 10 (Si 2 O 7 ) 4 (OH,F,O) 10 [36], does not explicitly show the occupancies of the Y1 site. This simplified formula is now out of date since it refers to five vesuvianite-group minerals: vesuvianite sensu stricto, manganvesuvianite, cyprine, magnesiovesuvianite and alumovesuvianite.…”