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pressures between 0.6 and 0.7 GPa, it breaks down to wollastonite and merwinite.
Akermanite and gehlinite have a continuous solid solution relationship (Ferguson
and Buddington 1920; Osborn and Schairer 1941). Sodamelilite is stable only
above 0.4 GPa (Kushiro 1964), and at lower pressure it breaks down to nepheline
and wollastonite.
Stopa et al. (2002) described the occurence of melilite-carbonetite rocks from the
Apennines of Italy, where the rocks have paragenetic relationship with kamafugites
of Grotto del Cervo, Abruzzo.
New discovery of leucite melilitites occurring as small lava
flows and of kalsilite-
melilite pyroclastic ejecta has been described from Monte
ascone Volcanics com-
plex of Roman Magatic Province of Central Italy by Di Battistini et al. (2001).
2.12 Ha
yne
ü
The chemical composition of Ha
yne lies between nosean (Na
8
Al
6
Si
6
O
24
SO
4
) and
a hypothetical end member (Ca
4
Al
6
Si
6
O
24
.SO
4
). It has a cubic symmetry. Some
ha
ü
ynes have minor replacements of Al by Fe
3+
but the substitution of K for Na is
more important in ha
ü
ü
yne.
This mineral occurs in potassic lavas of the Roman province, central Italy
(Table
2.11
). At Melfi,
yne
often displays chemical zoning and its alumina content increases towards the core
(De Fino et al. 1986). It has also been reported from phonolitic rocks at Sabatini by
Cundari (1979). It occurs as
,ha
ü
ynes have a relatively high content of K
2
O. Ha
ü
“
murky
”
phenocrysts with characteristic reddish rims.
yne is a very common feldspathoid, where it
occurs together with smaller amounts of leucite. Nepheline is present only as a
groundmass phase in melilite-bearing rocks, and is very rare in the feldspar-bearing
rocks.
Black oriented inclusions are often noted in ha
In the Mt. Vulture volcanic rocks ha
ü
ü
yne, where it is often concen-
trated towards the rims. It often has a thin
film at the outer rim which is inclusion-
free, and has large core-to-rim and
variations. The SO
3
concentra-
tion varies from 11.6 to 6.78 wt%, with a clear decrease of SO
3
content from the
core to the rim. Melluso et al. (1996) suggested frequent substitution of SO
3
by Cl,
which is coupled with Na-enrichment. This gives evidence for increasing sodalite
contents. K and Ca do not show clear trends, even though the most Ca
“
inter-sample
”
K, and Sr-
-
rich ha
ynes are found in relatively poorly differentiated samples (basanites and
tephrites). The ha
ü
ynes of the phonolites are characterised by low Ca, K and SO
3
contents, decreasing towards the rims and/or to the groundmass. In melilite-bearing
rocks however,
ü
ynes have sulphur. Caterina melilite-mela-foidite show
relatively high Ca and K contents coupled with low SO
3
(7 wt%). The Melfi
the ha
ü
ü
ha
ynophyre shows a higher variation in K
2
O(SO
3
content varying from 6.60 to
1.8 wt%) but without coherent trends from core to the rim (De Fino et al. 1986).
Di Muro et al. (2004) studied hauynophyre bearing lava from Mount Vulture
Italy. They collected a sample from a parasitic vent of the Vulture stratovolcano.
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