. Bulletin of the British Museum (Natural History), Mineralogy. AND KANGANKUNDE, MALAWI 209 vein rocks indicates that they have been subjected to chemical changes more akin to those which promote the development of the feldspathic breccias than the syenitic fenites. DISCUSSION Before considering some of the genetic aspects of fenitization in the Chilwa Series, some clarification of the nomenclature of fenites, as used in this account, is needed. Three quite distinct major processes, and a number of minor ones, are commonly. Fig. 8. Composite plot of fenite analyses in the system Qz-Ne-Ks. O =
. Bulletin of the British Museum (Natural History), Mineralogy. AND KANGANKUNDE, MALAWI 209 vein rocks indicates that they have been subjected to chemical changes more akin to those which promote the development of the feldspathic breccias than the syenitic fenites. DISCUSSION Before considering some of the genetic aspects of fenitization in the Chilwa Series, some clarification of the nomenclature of fenites, as used in this account, is needed. Three quite distinct major processes, and a number of minor ones, are commonly. Fig. 8. Composite plot of fenite analyses in the system Qz-Ne-Ks. O = country rocks; ^ = quartz fenites; ⢠= syenitic fenites; â = ultra-potassic fenites; â¡ = nepheline- bearing fenites. referred to the omnibus term fenitization, and certain aspects pertaining to the nature of these three branches of fenitization can be illustrated by Text-fig. 12. This diagram has been constructed from the data presented in Text-fig. 8, which incorporates a high proportion of the chemical data on fenites published to date. On Text-fig. 12, three metasomatic processes are considered: fenitization proper; feldspathization (as used by Garson & Campbell Smith, 1958), and nephelinization. It seems reasonable to distinguish these three processes because each one is chemi- cally and mineralogically distinctive, and, as will be discussed shortly, they are often associated with different groups of magmatic rocks:â Fenitization is promoted by syenites, nepheline syenites, ijolites, carbonatites. Nephelinization is promoted by nepheline syenites, ijolites, carbonatites(P).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)
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