Phase Relations in the System Leucite-Akermanite-Albite-SiO - Origin of Potassium-rich Silica-deficient Igneous Rocks - page 341

Fig. 11.9 Phase relationships
in the join leucite-akermanite-
albite at one atmospheric
pressure (Dwivedi et al. 2007)

Fig. 11.10 Phase
relationships in the join
leucite-akermanite-
albite 50 anorthite 50 at one
atmospheric pressure

anorthite is added, the primary phase field of diopsid ss shrinks considerably. In the

join leucite- akermanite-albite 50 An 50, one four phase point occurs at Lc 14 Ak 48
(Ab 50 An 50 ) 38 at 1,260

± °

5 C (point C) and the other occurs at Lc 15 Ak 35

± °

(Ab 50 An 50 ) 50 at 1,240 C (point D). At C, melilite, leucite ss and diopside ss

(equivalent to a rock called, melilite leucitite) are in equilibrium with liquid,
whereas at D, diopside ss leucite ss and plagioclase coexist with liquid (equivalent to
a rock, called leucite tephrite).
Electron microprobe analyses of plagioclase coexisting with leucite show the
following compositions: An 60 Ab 26 Or 14 ,An 66 Ab 17 Or 17 and An 64 Ab 21.6 Or 14.4 .
The analyses of plagioclase show that they are anorthite- rich as suggested by
Shand (1943). In most of the leucite- bearing tephrites, plagioclase has been found

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