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(Holmes 1950; Rogers et al. 1998), the Colli Albani complexes (Aurisicchio et al.
1988) and in Hawaii (Yoder and Tilley 1962), feldspathoid-bearing rocks are
associated with quartz-bearing trachyandesite or latite series of rocks. These
SiO
2
-
saturated varieties and feldspathoid-bearing rocks are apparently part of dif-
ferent volcanic cycles issued from the some magma chamber. The genesis of these
two contrasting varieties of lava is possibly controlled by the shifting of the thermal
barrier as a function of pressure and temperature (also see Yoder and Tilley 1962).
Jadeite-bearing amygdules have been recorded from a ma
c extrusive rock
occurring northwest of Kamchatka by Ponomareva and Dobretsov (1965). The
occurrence of jadeite suggests a deep-seated origin for the magma. Jadeite occurs in
association with nepheline in a rock from Tibet (Bauer 1896; Lacroix 1930). The
rock was also studied by Tilley (1956, also see Deer et al. 1997) , who reported that
jadeite crystals were traversed by nepheline. The latter also occurs together with
albite and jadeite in a troctolite from equatorial Paci
c.
A jadeite-, K-feldspar- and quartz bearing assemblage similar to the subsolidus
assemblage jadeite
K-feldspar has been reported from meta-morphosed
felsic magmatic rocks (e.g. metagranite) by Compagnoni and Maffeo (1973) from
Mt. Mucrone in the western Italian Alps. Such assemblages have also been reported
from the Alpine region of Acceglio, in Italy, by Lef
—
albite
—
è
vre and Michard (1965). Okey
—
(1997) described jadeite
and K-feldspar-bearing rocks from the Bektaslar region,
located west of Hormancik town, 60 km south of Busla, in Turkey (also see Deer
et al. 1997). The rocks underwent metamorphism, the P-T
T conditions of which are
similar to those of blue-schist facies. The modal percentage of jadeite, K-feldspar
and quartz with or without albite is plotted in Fig.
7.9
. The occurrence of jadeite
along with K-feldspar and quartz indicates the high-pressure crystallization of the
rocks, the bulk composition of which lies in the jadeite
-
silica subsys-
tem. The results of Gupta et al. (2010) at 2 GPa [P (H
2
O) = P (Total)] suggest that
the observed subsolidus assemblage justi
—
sanidine
—
es their presence along with glaucophane
in the blueschist facies. Osborne (1930) and Gummer and Burr (1946) have
reported the occurrence of nepheline-albite together with jadeite in the gneissic
rocks in the southern Grenville province of the Canadian shield (see also Appleyard
1969). In the Franciscan blueschist terrane, California, Ernst et al. (1970) reported
the occurrence of albite and quartz along with sodium-rich pyroxene containing
70
90 mol. % jadeite. With reference to the diagram of Gupta et al. (2010, Fig.
7.8
),
the assemblage jadeite + alkali feldspar + quartz occurs as a subsolidus assemblage.
McBirney et al. (1967) observed the occurrence of jadeite along with albite and
quartz from the Motagua fault zone of Guatemala. Such jadeite may be related to
the breakdown of albite at higher pressures. Chihara (1971) described the occur-
rence of jadeite from Mt. Osha at Oya, in Hyogo Prefecture, and Wakasa, in Tottori
prefecture, Japan. At Sambagawa in the Kamuiketan belt of Hokkaido, Seki (1960)
observed the occurrence of jadeite along with albite. Such an occurrence has also
been reported from Kotaki, Japan, by Iwao (1953) in a narrow (20 cm) zone around
an albite-rich core. The occurrence of jadeite and albite in these localities is con-
sidered by those authors to be of metamorphic origin.
-
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