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Fig. 3.14 composition plot
of kimberlites, lamproites and
lamprophytes in terms of
K
2
O
-
Mgo
-
Al
2
O
3
(after
bagman 1987)
3.3.2 Distinctive Criteria to Differentiate Among Kimberlites,
Lamproites and Lamprophyres
Bagman (1987) plotted the compositions of Kimberlites, lamproites and lampro-
phytes in terms of K
2
O, MgO and Al
2
O
3
(Fig.
3.14
) and showed that their com-
positions plot in three distinct
fields through there are some overlaps.
Whereas kimberlites do not contain such minerals as leucite, melilite, wadeite,
priderite there are magnesium rich lamproites which may contain diamond like the
kimberlites suggesting their high pressure origin, whereas felspathoide-bearing
lamproites were crystallized at relatively low pressure inside the crust. Although
presence of K-richterite was considered as an index mineral (Kushiro and Erlank
1970)
to identify lamproites,
recent studies at high pressure-temperature on
K-richterite suggest
that
these mineral
is stable at a signi
cant depth, where
diamond is also stable.
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