The Crystal Chemistry of Nepheline

Abstract

The crystal structures of three nepheline samples, (1) , from the Khibina-Lovozero complex, Kola Peninsula, Russia, (2) , from Monte Somma, Italy, have been refined to R 1 indices of 1.8, 2.7 and 1.7% using 1273, 1191 and 1364 unique observed (| F o | > 4F) reflections collected with a single-crystal diffractometer and MoK␣ X-radiation. No superstructure reflections were observed. Viewed down [001], the aluminosilicate tetrahedra occur at the vertices of a 6 3 net in which there are two distinct types of six-membered rings of tetrahedra: one quarter are nearly regular hexagonal rings centered on (0, 0, z), whereas the other three-quarters are flattened hexagonal rings centered on 0 ½ z. In both rings, the tetrahedra have the sequence ududud, and linkage up and down c forms a four-connected three-dimensional framework. The A site is located in the channel along 0 0 z and is [9]-coordinated by oxygen atoms between 2.97 and 3.04 Å; <A-O> = 2.999, 3.009 and 3.008 Å for samples 1, 2 and 3, respectively. The A site is fully occupied by K in nepheline (1), and it is partly occupied by K (0.80 and 0.88) in samples (2) For the nepheline sample from the Khibina-Lovozero complex, the simplified chemical formula, K 2 Na 6 Si 8 Al 8 O 32 , corresponds to the ideal end-member formula of nepheline with the A site fully occupied by K, the B site fully occupied by Na, and Si and Al completely ordered at the T sites. This sample crystallized in a hyperagpaitic rock formed at the last stages of low-temperature pneumatolitic activity. Nepheline (2), also formed in low-temperature pegmatitic environment, shows very high Al-Si order at the T sites. The Monte Somma nepheline is of high-temperature origin. Previous refinements of the structure had indicated a fairly disordered Al-Si distribution for it. The present results indicate maximal Al-Si order, in accord with previous 29 Si MAS NMR results. Our results suggest that nepheline exhibits maximal Al-Si order irrespective of temperature of origin of the nepheline.Keywords: nepheline, cation ordering, end-member composition, Khibina-Lovozero, Russia, Bancroft, Canada, Monte Somma, Italy. SOMMAIRENous avons affiné la structure cristalline de trois échantillons de néphéline, (1) Mots-clés: néphéline, mise en ordre des cations, composition du pôle,

Crystal chemistry of K-rich nepheline in nephelinite from Hamada, Shimane Prefecture, Japan

“…Hahn and Buerger (1955) reported <T3-O> and <T4-O> distances of 1.675 and 1.685 Å, respectively, for volcanic nepheline from Monte Somma, implying a high degree of Al-Si disorder in the T3 and T4 sites. However, their data have not been supported by subsequent studies of nepheline at the same locality by Simmons and Peacor (1972), Tait et al (2003) and Balassone et al (2014) (Table 7). Thus, the T-O distances reported by Hahn and Buerger (1955) seem to be invalid.…”

“…Possible factors controlling the three mechanisms need to be clarified by further study. Symbols and sources: circles (Balassone et al, 2014), square (Vulić et al, 2011), triangle (up) (Antao and Hassan, 2010), triangle (down) (Angel et al, 2008), triangle (left) (Tait et al, 2003), triangle (right) (Hassan et al, 2003), diamond (Simmons and Peacor, 1972), hexagon (Foreman and Peacor, 1970), narrow diamond (Dollase, 1970).  min (eÅ -3 ) -0.58 at 0.14 Å from T1 *1 X-ray diffraction data were collected using a Bruker SMART APEX II CCD difractometer at Shimane University, using graphite-monochromatized MoK radiation ( = 0.71069 Å).…”

Glass Composition Constraint Recommendations for Use in Life-Cycle Mission Modeling

“…The presence of boron has been shown to reduce the tendency toward nepheline formation (Li et al 2003), and there is some evidence that CaO also reduces the tendency. Some recent studies have deliberately varied CaO and B 2 O 3 levels in waste glass formulations to attempt to understand these phenomena (Fox et al 2007 and2008 (Tait et al 2003, Palmer 1994, and Duke et al 1967). …”

Geologia e Petrologia da suíte alcalina de Bom Repouso, MG

“…É formada por um esqueleto de tetraedros de sílica e alumina com os cátions alcalinos nos interstícios. O sítio A é geralmente ocupado por 2/3 de K e 1/3 vacante, enquanto o sítio B é completamente ocupado por Na, podendo entrar um pouco de Ca, e o sítio T por Al e Si, além de algum Fe 3+ (Dollase & Peacor, 1971;Dollase & Thomas, 1978;Tait et al, 2003) Possui uma fórmula ideal (Na 3 KAl 4 Si 4 O 16 ) representada por uma composição intermediária entre os membros finais Ne -nefelina, NaAlSiO 4 , e Ks -kalsilita, KAlSiO 4 , através da substituição Na ↔ K (Buerger et al, 1954;Hahn & Buerger, 1955 (Bailey & Schairer, 1963;Onuma et al, 1972).…”

“…Hamilton, 1961;Deer et al, 1992;Holvis & Roux, 1993;Tait et al, 2003;Holvis et al, 2009). O outro é representado por Na 2 O -Fe 2 O 3 -Al 2 O 3 -SiO 2 , com os membros finais Ne, FeNe e Qz (e.g.…”