perthite


Also found in: Encyclopedia, Wikipedia.

perthite

(ˈpɜːθaɪt)
n
(Geological Science) mineralogy a type of feldspar that contains both a potassium type (orthoclase) and a sodium type (albite)
Mentioned in ?
References in periodicals archive ?
In the complex microprophries is very fine grained with orthoclase, perthite, quartz, biotite, magnetite, epidote as major minerals.
Chl: chlorite film; Sty: stylolite; Pri: primary pore; Pert: perthite; Orth: orthoclase; I/S: illite-smectite mixed-layer clays; Shri: shrinkage; AQ: authigenic quartz; Cal: calcite cement; F: Feldspar; InterD: interparticle dissolution pores; IntraD: intraparticle dissolution pores; Tuff: tuffaceous; Diss: dissolution pores; K: kaolinite; I: illite.
Plagioclase ranges from (23.8% -45.6%) Microcline often intergrown graphically and are sometimes perthitic with albite occurring as patchy perthite. It however displays cross hatch twinning.
Microfractures in the perthite grains contain fine-grained alkali feldspar.
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.
Exiled Perthite Brian Thomson from Kettering said: "Tam Cowan's comments about the size of St Johnstone's crowds were out of order.
The body is occupied by petrographically uniform granite composed of perthite, albitic plagioclase, quartz, and small quantities of biotite, opaque oxide and titanite.
1) 2) 3) 4) 5) Quartz 30 35 34 28 - alkali feldspar 60 57 63 58 - (perthite) calcic - - - - 49 plagioclase Biotite <1 <1 - 1 1 alkali 9 8 6 11 - amphibole calcic - - - - 26 hornblende Clinopyroxene - - - - 9 Orthopyroxene - - - - 7 Olivine - - - - 3 Ore - <1 - 1 4 Accessory 1 <1 <1 1 1 minerals IUGS rock a-fG a-fG a-fGl a-fG G-N classification Abbreviations: a-fG = alkali-feldspar granite.
(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).
It is occupied by petrographically uniform granite composed of perthite, sodic plagioclase, quartz, and small quantities ofbiotite, opaque oxide and titanite.