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A Study of a Deep Weathering Profile on Granite in Peninsular Malaysia: III. Alteration of Feldspars
Author(s) -
Eswaran H.,
Bin Wong Chaw
Publication year - 1978
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1978.03615995004200010034x
Subject(s) - pseudomorph , gibbsite , kaolinite , halloysite , weathering , biotite , geology , mineral , feldspar , mineralogy , geochemistry , bauxite , quartz , materials science , metallurgy , paleontology
Feldspar grains or their pseudomorphs from the different weathering zones are studied with the SEM. Weathering commences with dissolution to form voids in the grains. Close to the rock, the first product is allophanic material present as globules adhering to the voids in the grains. In the δ zone the product is halloysite with some amorphous silica spherules. The surface of the pseudomorph has a hummocky appearance suggesting an amorphous intermediary phase prior to halloysite formation. Kaolinite formation commences in the γ p zone and gibbsite in the γ m zone. Admixtures of kaolinite and halloysite may be found on the same pseudomorph, but admixture of gibbsite with another secondary mineral is not encountered. Biotite follows a similar trend of alteration. It is concluded that irrespective of the primary weatherable mineral, the type of secondary mineral found is a function of the microenvironment.