iddingsite

iddingsite

[′id·iŋ‚zīt]
(mineralogy)
A reddish-brown mixture of silicates, forming patches in basic igneous rocks.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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D'Antonio and Kristensen (2005) analysed the secondary minerals generated by hydrothermal alteration affecting the basalts of oceanic crust in the West Philippine Sea Basin and recorded clay minerals, mostly glauconite, minor Al-saponite and Fe-beidellite, together with iddingsite, Ca-Na zeolites and calcite.
Composition measurements of the Y000593 spherules show that they are significantly enriched in carbon compared to the nearby surrounding iddingsite layers.
The olivine is partially to completely replaced by antigorite and iddingsite and the orthopyroxene is generally replaced by antigorite, bastite and chlorite.
The olivine (Fo92-94) is partially to completely replaced by antigorite or occasionally altered to iddingsite. Chrysotile veinlets generally cross cut the groundmass.
Moreover, its phenocrystal unity is a compound of plagioclase, kaersutite, iddingsite olivine minerals.
Iddingsite, calcite, serpentine, and zeolite are the main secondary minerals.
Olivine is mostly fresh, but in some cases it is altered to iddingsite and/or serpentine.
Alteration of both phenocrysts and groundmass is also evident in most sections, with olivine partly or totally altered to iddingsite, and plagioclase weathering to clay minerals.
Olivine occurs in nearly ail cumulates as sub- to anhedral grains, and is partly altered to serpentine or iddingsite. In more evolved cumulates, clinopyroxene is modally abundant, and is generally partly altered to green amphibole.
The latter minerals are surrounded by red iddingsite rims (samples no.
Swindle of the University of Arizona in Tucson and his colleagues, contains an abundance of iddingsite, a mixture of clays and iron oxides that forms only in the presence of water.