Mineralogy - Origin of Potassium-rich Silica-deficient Igneous Rocks - page 61

Fig. 2.16 The distribution of
Ba + Cr and Ti + K in
priderites. Solid circles:
Smoky Butte lamproite,
Montana; plus symbol,
priderite from Sisco minette,
Corsica, (France); solid
triangles: priderite from
wolgidite, Mount North, West
Kimberley; solid squires:
Leucite Hillis lamproite (after
Wagner and velde 1986)

1.2

0.8

0.4

6.8 7.2 7.6 8.0 8.4

Ti + K

priderite from Leucite Hills contains more Ba than that from West Kimberley. They
may have a solid solution relationship between K-priderite and Ba-priderite
(Norrish 1951). Priderite in association with ilmenite is observed in Mt. North
lamproite from Australia and Sisco Minette from Corsica (Wagner and Velde
1986). Analyses of priderites show that (Ba + Cr) has a negative correlation with
respect to (Ti + K, Fig. 2.16 ).
Smoky Buttte lamproites often contain priderites (Post et al. 1982). It is enriched
in Ba (up to 0.85), but K is only 0.4 per formula unit. It contains 4.3 wt% Cr 2 O 3 in
West Kimberley and Smoky Butte lamproites, respectively, but it can be Cr-poor
also (<0.3 wt%, Table 2.14 ). The high Ba values suggest the existence of Ba end
member of the priderite series.
This mineral has also been described as an accessory phase from lamproitic
rocks of Mohanpur (West Bengal, India; Gupta et al. 1983), and Kapamba,
Luangwa valley (eastern Zambia, Scott Smith et al. 1987).

2.16 Wadeite

Prider (1939) described wadeite for the first time from K-rich rocks of West

Kimberley province. Henshaw (1955) determined its crystal structure, and found
that it has hexagonal symmetry and high birefringence. Its ideal formula is
Zr 2 K 4 Si 6 O 18 . The structure is constituted of rings of (Si 2 O 9 ) 6 − , similar to benitoite.
It is also present (Table 2.15 ) as an accessory mineral in the ultrapotassic rocks of
Leucite Hills (Carmichael 1967).