perthite


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perthite

(ˈpɜːθaɪt)
n
(Geological Science) mineralogy a type of feldspar that contains both a potassium type (orthoclase) and a sodium type (albite)
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The body is occupied by petrographically uniform granite composed of perthite, albitic plagioclase, quartz, and small quantities of biotite, opaque oxide and titanite.
6%) Microcline often intergrown graphically and are sometimes perthitic with albite occurring as patchy perthite.
The type locality for perthite, for instance, now lies buried beneath a highway in Ontario.
Rock type An (4) Zoning (5) Leucogranite < 5 unzoned non- exsolved Fine-grained luecomonzogranite Coarse-grained zoned > patch > luecomonzogranite unzoned rod & bead perthite Muscovite-bionte monzogranite Biotite monzogranite Biotite < 5 - 35 zoned rod granodiorite & bead perthite Cord.
Late recrystallization of magmatic sanidine resulting in perthite formation supposedly did not take place because the rocks have not been heated more than 50-100[degrees]C during the geological history, as indicated by the alteration index of conodonts, which varies between 1 and 2 in the Silurian and Ordovician rocks of Estonia (Mannik & Viira 1990).
Exiled Perthite Brian Thomson from Kettering said: "Tam Cowan's comments about the size of St Johnstone's crowds were out of order.
It is occupied by petrographically uniform granite composed of perthite, sodic plagioclase, quartz, and small quantities ofbiotite, opaque oxide and titanite.
3) Rischorrite is a variety of nepheline syenite in which nepheline is poikilitically enclosed in microcline perthite (Jackson, 1997).
The granodiorite is a relatively undeformed, medium-grained, and slightly porphyritic, and contains intensely sausseritized plagioclase in an equigranular matrix of similarly altered, finer grained plagioclase, perthite, quartz, and equant to interstitial biotite and possibly amphibole (both now chlorite).
The granite is composed of perthite quartz some plagioclase opaque oxide biotite and/or amphibole and titanite whereas the quartz monzonite comprises perthite calcic oligoclase/andesine quartz and minor amount of mafic minerals similar to those of the granite.
Rischorrite: A variety of nepheline syenite in which nepheline is poikilitically enclosed in microcline perthite.
Alkali feldspar laths up to 4 mm in length with patch perthite texture (Fig.