iddingsite

iddingsite

[′id·iŋ‚zīt]
(mineralogy)
A reddish-brown mixture of silicates, forming patches in basic igneous rocks.
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References in periodicals archive ?
Few olivine crystals can be identified in the thin section and they show oxidized rounded borders and alteration to iddingsite, suggesting that they may be xenocrysts instead of phenocrysts from the new batch of magma.
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.
Moreover, its phenocrystal unity is a compound of plagioclase, kaersutite, iddingsite olivine minerals.
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.
The lherzolite is composed of olivine (mostly altered to iddingsite and serpentine) enclosed by blurry clinopyroxene oikocrysts.
The latter minerals are surrounded by red iddingsite rims (samples no.
9 olivine phenocrysts are overgrown by red iddingsite rims.
Analyzing 10 samples of the meteorite by radioactive dating, the team found that the iddingsite formed between 274 and 655 million years ago.