Baggalútar from Hvalfjörður (Iceland): Enigmatic spheroids of hydrothermally altered basaltic tephra
Baggalútar are well-rounded spheroids that typically measures 16-18 mm in size and have a brownreddish appearance. They can be found in the Hvalfjörður bay in SW Iceland. There are manydescriptions in literature and on the internet that Baggalútar are volcanic spherulites formed by quartzor cristoba...
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Uppsala universitet, Mineralogi, petrologi och tektonik
2022
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ftuppsalauniv:oai:DiVA.org:uu-477339 2023-05-15T16:47:45+02:00 Baggalútar from Hvalfjörður (Iceland): Enigmatic spheroids of hydrothermally altered basaltic tephra Baggalútar från Hvalfjörður (Island): Gåtfulla sfäroider av hydrotermiskt omvandlad basaltisk tefra Djuse, Emmie 2022 application/pdf http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-477339 eng eng Uppsala universitet, Mineralogi, petrologi och tektonik Självständigt arbete vid Institutionen för geovetenskaper 2022: 4 http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-477339 info:eu-repo/semantics/openAccess Baggalútar Iceland basalt Hvalfjörður zeolites volcanic spherulite spheroids Island zeoliter vulkaniska sfäruliter sfäroider Geology Geologi Student thesis info:eu-repo/semantics/bachelorThesis text 2022 ftuppsalauniv 2023-02-23T22:01:17Z Baggalútar are well-rounded spheroids that typically measures 16-18 mm in size and have a brownreddish appearance. They can be found in the Hvalfjörður bay in SW Iceland. There are manydescriptions in literature and on the internet that Baggalútar are volcanic spherulites formed by quartzor cristobalite spheres growing out of a common centre and there is also a broadly accepted consensusof this theory. However, despite this consensus that Baggalútar are volcanic spherulites there exist nodetailed investigation of their origin. The aim of the thesis is to investigate what Baggalútar is exactlyand how they form. This is achieved by using a combination of petrographic observations with apolarization microscope, mineral chemistry from electron microprobe analysis and measurements oftheir magnetic properties. The results are compared with different geological and anthropological spheroids, spherulites,nodules and concretions. The petrographic observations show that they predominantly consist of finegrained basaltic tephra (groundmass) together with zeolites infilling voids. Analyses of mineralchemistry indicate that the groundmass consists of augitic pyroxene, plagioclase, and two differentoxides where one classifies as titanomagnetite. The magnetic measurements support this by showing aCurie temperature at approximately 460-470 °C which is likely to be titano-magnetite. Although thedifferent geological and anthropological processes that typically results spheroidal shapes have somesimilarities that could explain the formation of baggalútar, most of these can be excluded for differentreasons. The internal textures of baggalútar strongly indicate that the shape is controlled by externalfactors, like weathering or erosion from beach outcrops. This could explain the spherical shape of asingle baggalút, but it fails to explain the spheroidal shapes of individual baggalútar joined together inclusters. Baggalútar är väl rundade sfäroider som vanligtvis mäter 16–18 mm i storlek och har ett brunt rödaktigtutseende. De ... Bachelor Thesis Iceland Uppsala University: Publications (DiVA) Hvalfjörður ENVELOPE(-21.663,-21.663,64.376,64.376) |
institution |
Open Polar |
collection |
Uppsala University: Publications (DiVA) |
op_collection_id |
ftuppsalauniv |
language |
English |
topic |
Baggalútar Iceland basalt Hvalfjörður zeolites volcanic spherulite spheroids Island zeoliter vulkaniska sfäruliter sfäroider Geology Geologi |
spellingShingle |
Baggalútar Iceland basalt Hvalfjörður zeolites volcanic spherulite spheroids Island zeoliter vulkaniska sfäruliter sfäroider Geology Geologi Djuse, Emmie Baggalútar from Hvalfjörður (Iceland): Enigmatic spheroids of hydrothermally altered basaltic tephra |
topic_facet |
Baggalútar Iceland basalt Hvalfjörður zeolites volcanic spherulite spheroids Island zeoliter vulkaniska sfäruliter sfäroider Geology Geologi |
description |
Baggalútar are well-rounded spheroids that typically measures 16-18 mm in size and have a brownreddish appearance. They can be found in the Hvalfjörður bay in SW Iceland. There are manydescriptions in literature and on the internet that Baggalútar are volcanic spherulites formed by quartzor cristobalite spheres growing out of a common centre and there is also a broadly accepted consensusof this theory. However, despite this consensus that Baggalútar are volcanic spherulites there exist nodetailed investigation of their origin. The aim of the thesis is to investigate what Baggalútar is exactlyand how they form. This is achieved by using a combination of petrographic observations with apolarization microscope, mineral chemistry from electron microprobe analysis and measurements oftheir magnetic properties. The results are compared with different geological and anthropological spheroids, spherulites,nodules and concretions. The petrographic observations show that they predominantly consist of finegrained basaltic tephra (groundmass) together with zeolites infilling voids. Analyses of mineralchemistry indicate that the groundmass consists of augitic pyroxene, plagioclase, and two differentoxides where one classifies as titanomagnetite. The magnetic measurements support this by showing aCurie temperature at approximately 460-470 °C which is likely to be titano-magnetite. Although thedifferent geological and anthropological processes that typically results spheroidal shapes have somesimilarities that could explain the formation of baggalútar, most of these can be excluded for differentreasons. The internal textures of baggalútar strongly indicate that the shape is controlled by externalfactors, like weathering or erosion from beach outcrops. This could explain the spherical shape of asingle baggalút, but it fails to explain the spheroidal shapes of individual baggalútar joined together inclusters. Baggalútar är väl rundade sfäroider som vanligtvis mäter 16–18 mm i storlek och har ett brunt rödaktigtutseende. De ... |
format |
Bachelor Thesis |
author |
Djuse, Emmie |
author_facet |
Djuse, Emmie |
author_sort |
Djuse, Emmie |
title |
Baggalútar from Hvalfjörður (Iceland): Enigmatic spheroids of hydrothermally altered basaltic tephra |
title_short |
Baggalútar from Hvalfjörður (Iceland): Enigmatic spheroids of hydrothermally altered basaltic tephra |
title_full |
Baggalútar from Hvalfjörður (Iceland): Enigmatic spheroids of hydrothermally altered basaltic tephra |
title_fullStr |
Baggalútar from Hvalfjörður (Iceland): Enigmatic spheroids of hydrothermally altered basaltic tephra |
title_full_unstemmed |
Baggalútar from Hvalfjörður (Iceland): Enigmatic spheroids of hydrothermally altered basaltic tephra |
title_sort |
baggalútar from hvalfjörður (iceland): enigmatic spheroids of hydrothermally altered basaltic tephra |
publisher |
Uppsala universitet, Mineralogi, petrologi och tektonik |
publishDate |
2022 |
url |
http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-477339 |
long_lat |
ENVELOPE(-21.663,-21.663,64.376,64.376) |
geographic |
Hvalfjörður |
geographic_facet |
Hvalfjörður |
genre |
Iceland |
genre_facet |
Iceland |
op_relation |
Självständigt arbete vid Institutionen för geovetenskaper 2022: 4 http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-477339 |
op_rights |
info:eu-repo/semantics/openAccess |
_version_ |
1766037868467191808 |