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Grön fältspat i Varbergskomplexet

Schönherr, Lara LU (2022) In Examensarbeten i geologi vid Lunds universitet GEOL01 20221
Department of Geology
Abstract (Swedish)
Den kända Varbergscharnockiten från Hallandskusten är en granitisk, pyroxenförande bergart som har både magmatiska och metamorfa drag. Bergarten har deformerats och omkristalliserats under högmetamorfa förhållanden men har sannolikt redan sedan den ursprungliga kristallisationen varit pyroxenförande. Olikt andra granitiska bergarter är Varbergscharnockiten mörkt grågrön. Denna färg orsakas av fältspat, som tillsammans med kvarts, pyroxen och hornblände är charnockitens dominerande mineral. Efter att fyra tunnslip, tre charnockiter och en deformerad pegmatit, från olika delar av Varbergskomplexet analyserats med polarisationsmikroskop och svepelektronmikroskop (SEM-EDS) visade sig fältspaten i charnockiten bestå av antipertitisk plagioklas,... (More)
Den kända Varbergscharnockiten från Hallandskusten är en granitisk, pyroxenförande bergart som har både magmatiska och metamorfa drag. Bergarten har deformerats och omkristalliserats under högmetamorfa förhållanden men har sannolikt redan sedan den ursprungliga kristallisationen varit pyroxenförande. Olikt andra granitiska bergarter är Varbergscharnockiten mörkt grågrön. Denna färg orsakas av fältspat, som tillsammans med kvarts, pyroxen och hornblände är charnockitens dominerande mineral. Efter att fyra tunnslip, tre charnockiter och en deformerad pegmatit, från olika delar av Varbergskomplexet analyserats med polarisationsmikroskop och svepelektronmikroskop (SEM-EDS) visade sig fältspaten i charnockiten bestå av antipertitisk plagioklas, vilken består av oligoklas med avblandningsdomäner av K-fältspat, samt grå mikropertitisk K-fältspat, vilken sannolikt är ortoklas. Pegmatitens fältspater består av Na-bärande albit och röd K-fältspat, där albiten har bekräftats vara grön. Orsaken till den grönaktiga färgen hos plagioklasdomänerna har inte kunnat fastställas. Det är möjligt att fältspaten i Varbergscharnockiten färgas likt andra fältspater, nämligen genom spårämnen eller defekter i kristallstrukturen som genom excitation av elektroner absorberar vissa våglängder av inkommande ljus och därmed framhäver en viss färg. (Less)
Abstract
The well-known Varberg charnockite from the coast of Halland in southern Sweden is a granitic, pyroxene-bearing rock which has both magmatic and metamorphic features. The rock has been deformed and recrystallized at high temperature and pressure but has probably been pyroxene-bearing since the original crystallization. Unlike other granitic rocks the Varberg charnockite has a dark grey green colour. The greenish colour is caused by feldspars, which in addition to quartz, pyroxene and hornblende are the predominant minerals in charnockite. Four thin sections, three charnockites and one deformed pegmatite, from different parts of the Varberg complex were analyzed using polarization microscopy and scanning electron microscopy (SEM-EDS). The... (More)
The well-known Varberg charnockite from the coast of Halland in southern Sweden is a granitic, pyroxene-bearing rock which has both magmatic and metamorphic features. The rock has been deformed and recrystallized at high temperature and pressure but has probably been pyroxene-bearing since the original crystallization. Unlike other granitic rocks the Varberg charnockite has a dark grey green colour. The greenish colour is caused by feldspars, which in addition to quartz, pyroxene and hornblende are the predominant minerals in charnockite. Four thin sections, three charnockites and one deformed pegmatite, from different parts of the Varberg complex were analyzed using polarization microscopy and scanning electron microscopy (SEM-EDS). The results showed that the feldspars in the charnockite are antiperthitic plagioclase, which consists of oligoclase with exsolved K-feldspar domains, and grey, micro-perthitic K-feldspar, which likely is orthoclase. The feldspars in the pegmatite mostly consist of Na-bearing albite and pink K-bearing orthoclase, where the albite has been confirmed to have a green colour. The cause of the greenish colour could not be determined. It is possible that the colour of the Varberg charnockite is caused by similar colour-causing mechanisms as in other feldspars. These include trace elements and defects in the crystal structure which through the excitation of electrons absorb specific wave lengths of incoming light and consequently cause the resulting colour. (Less)
Please use this url to cite or link to this publication:
author
Schönherr, Lara LU
supervisor
organization
course
GEOL01 20221
year
type
M2 - Bachelor Degree
subject
keywords
färg, charnockit, fältspat, Varberg, optisk mineralogi, geokemi
publication/series
Examensarbeten i geologi vid Lunds universitet
report number
636
language
Swedish
id
9087581
date added to LUP
2022-06-13 09:59:06
date last changed
2022-06-13 09:59:06
@misc{9087581,
  abstract     = {{The well-known Varberg charnockite from the coast of Halland in southern Sweden is a granitic, pyroxene-bearing rock which has both magmatic and metamorphic features. The rock has been deformed and recrystallized at high temperature and pressure but has probably been pyroxene-bearing since the original crystallization. Unlike other granitic rocks the Varberg charnockite has a dark grey green colour. The greenish colour is caused by feldspars, which in addition to quartz, pyroxene and hornblende are the predominant minerals in charnockite. Four thin sections, three charnockites and one deformed pegmatite, from different parts of the Varberg complex were analyzed using polarization microscopy and scanning electron microscopy (SEM-EDS). The results showed that the feldspars in the charnockite are antiperthitic plagioclase, which consists of oligoclase with exsolved K-feldspar domains, and grey, micro-perthitic K-feldspar, which likely is orthoclase. The feldspars in the pegmatite mostly consist of Na-bearing albite and pink K-bearing orthoclase, where the albite has been confirmed to have a green colour. The cause of the greenish colour could not be determined. It is possible that the colour of the Varberg charnockite is caused by similar colour-causing mechanisms as in other feldspars. These include trace elements and defects in the crystal structure which through the excitation of electrons absorb specific wave lengths of incoming light and consequently cause the resulting colour.}},
  author       = {{Schönherr, Lara}},
  language     = {{swe}},
  note         = {{Student Paper}},
  series       = {{Examensarbeten i geologi vid Lunds universitet}},
  title        = {{Grön fältspat i Varbergskomplexet}},
  year         = {{2022}},
}