Mineralogy - Origin of Potassium-rich Silica-deficient Igneous Rocks - page 20

contain 87 89 % orthoclase (Wagner and Velde 1986). The average Fe 2 O 3 content

of K-feldspars is 1

-

2 %, but it is slightly higher in the Moon Canyon lamproite
(2.5 %). Its concentration is as high as 0.62 % in Murcia lampoite and 1

-

3%in
Smoky Butte lamproite. In K-rich selagites from Orciatico (Italy) and Shiprock
dyke (Montana), the BaO content shows large variation, 0

-

0.89 % and 0.3 3.32 %,

- -

respectively.
Coexistence of sanidine with anorthoclase, pseudoleucite and leucite is noted in
shoshonitic and absarokitic rocks of Artem of Primorye district (north of Vlad-
ivostok), Russia. Here, K-feldspar constitutes 60

80 % of a potassic suite com-
prising nepheline, biotite, augite and amphibole (Borodin 1974). In many
pseudoluecite tinguaites, syenites, and minette dykes at Pamir, K-feldspar occurs as
a major phase (Dimitriev 1976). Sanidine is one of the major phases in the alkaline
complex of the Tezhser in Caucasus, where it occurs in leucite-bearing trachytes
and trachyandesites, where K-feldspar contains up to 10 % albite. Phase relations in
the system kalsilite

-

K-feldspar at 2 GPa and variable temperatures are shown in
Fig. 2.3 , indicating limited solid solution of kalsilite in K-feldspar. Extent of solid
solution of jadeite in K-feldspar (albite

-

— K-feldspar) and jadeite in nepheline

(nephiline — albite system) at 2 GPa and different temperatures are shown in

Figs. 2.4 and 2.5 , respectively.

Fig. 2.3 Phase relations
along the join kalsilite —
K-feldspar determined at 2
GPa [P(H 2 O) = P(Total)] and
various temperatures. The
solvus has been inferred from
EPMA data for subsolidus
runs (after Gupta et al. 2010)