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consisted of a
fine-grained inter-growths of nepheline and sanidine. According to
them, fresh leucites occur as inclusions within olivine and clinopyroxene grains.
This supports the idea that leucite appeared from these rocks as primary crystals,
but were converted to pseudoleucite due to metasomatic processes. As soda-rich
fluid could not diffuse through clinopyroxenes and olivines, those leucite grains
occurring as inclusion within these crystals survived.
Luhr and Giannetti (1987) studied leucite crystals from the Brown Leucitic Tuffs
of Roccamon
na, and observed that leucites are typically less than 2 mm across, but
reach 0.25 mm across in some pumices. Primarily leucite is rarely preserved in the
cores of larger crystals but secondary analcite crystals can retain primary radial
inclusion pattern. According to them analcitization of leucite is a common geo-
logical phenomenon in these tuffs.
Scott Smith et al. (1987) studied pseudoleucite from Kapamba lamproites of
sanidine and brown turbid grain with chemistry similar to that of analcite (SiO
2
: 52.
04 %, Al
2
O
3
:23.58 %, Na
2
O:11.89 wt%). A few pseudoleucites however, consisted
of sanidine and nepheline (SiO
2
:46.75 %, Al
2
O
3
: 25.77, Na
2
O: 25.53 wt%). These
minerals may occur in one grain showing similarity toward pseudoleucite, and all
these are pseudomorphous after leucite.
Mitchell et al. (1987) observed the presence of pseudoleucite from Smoky Butte,
Montana. Here, they observed the presence of analcite, which they think, are not
primary but are pseudomorphous after primary leucite phenocrysts. They supported
the experimental study of Gupta and Fyfe (1975), and considered that they were
formed by metasomatism of Na-rich
fluid by diagenetic process.
The phonolitic and tephritic lavas of Azerbaizan volcanics from northwestern Iran
were studied by Comin-Chiramonti et al. (1997). Analcite occurs in these extrusive
rocks as a devitri
cation product or as a secondary mineral. They considered their
formation due to complete transformation of possibly leucite by metasomatic pro-
cess. The fact that originally they were leucite is borne by the fact that a trace of
leucite could be found in the rim of the analcites, which were predominately potassic
with 15 % K
2
O, and having essentially analcitized core. Wilkinson (1977) consid-
ered that analcite phenocrysts of vitrophyric analcitite (similar to Razy glassy dike of
Azerbaijan) are possibly ion-exchanged leucites and conversion of leucite to analcite
must have been complete during hydration. According to Comin-Chiramonti et al.
the analcites occurring in the groundmass of tephri-phonolitic rocks of Sehjafarlu,
Azerbaijan were originally leucites, crystallized at low pressure of H
2
O. The bulk
composition of these analcites is similar to that of leucite.
Pseudoleucites from the Crowsnest formation of Canada and Colima volcanic
complex in Mexico were studied by Karlsson and Clayton (1991). They obtained
stable isotope (H, N, O), electron microprobe and ion microprobe data for analcites
from these two localities. They obtained isotope ratios of framework (
18
O
f
) and the
δ
18
O
cw
,
δ
δ
channel water (
D) for two Crowsnest samples and one Colima sample.
Both O and H isotopic ratios of channel water in all three samples, fall in the
meteoric water line, and de
18
O
f
values for
Crowsnest (13.6 and 14.2 %) and Colima (8.7 %) indicate that these analcite
nitely are not magmatic. The
δ
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