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Characterization of Megendi/Angatosch and Delanta Ethiopian gem opal-CT
2010 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

This study aims to describe the structure of Ethiopian gem opal-CT in order to characterize the material. Focus is made on gem opal-CT originating from Megendi/Angatosch in Gonder and Delanta in Wollo/Wello, both situated in the Amahara region, Ethiopia. This study also aims to describe the opal host rock by means of petrographic investigations in order to better understand the geological setting that hosts this poorly studied gem material. The analytical methods used in the study are optical microscopy, Raman spectroscopy and Extreme High Resolution Electron Scanning Microscopy. The dominant rock type is a mafic extrusive rock with trachytic (sanidine) and amygdule texture and contains phenocrysts of clinopyroxene, suggested to be a trachybasalt belonging to the Cenozoic “trap series”. The opal is precipitated from hydrothermal solutions within the amygdule accompanied by iron hydroxide situated at the rim of the amygdule, which precipitates before the formation the opal. The structure of the opal is built up by nano-grains with an average diameter of <10nm, probably 5-8nm. such a small particle diameter in opal is documented here for the first time. the nano- grains aggregate to form larger pseudo spheres, fundamental for the opal-play-of-colour to occur. the pseudo spheres are hosted in a matrix that react more heavily on 10% hf for 30 seconds than the pseudo spheres them self. this is documented here for the first time in gem opal-ct and indicates that opal-ct is a two phase material. the study shows that ethiopian gem opal-ct is a very interesting and complex material from a geological, mineralogical and gemmological point of view.

Place, publisher, year, edition, pages
2010.
Keyword [en]
Life Earth Science, Opal, Opal-CT, Ethiopia, Delanta, Megendi, Wollo, Gonder, structure, gem, gemmology, geology, mineralogy, characterization, Raman, Petrography, Extreme High Resolution, Scanning Electron Microscope, Nano particle, Christobalite, Tridymite, Luleå, opal play of colour, Ethiopian gem
Keyword [sv]
Bio- och geovetenskaper
Identifiers
URN: urn:nbn:se:ltu:diva-53117ISRN: LTU-PB-EX--10/033--SELocal ID: a2f87a38-6109-4e87-98f8-620e377c7365OAI: oai:DiVA.org:ltu-53117DiVA: diva2:1026491
Subject / course
Student thesis, at least 30 credits
Educational program
Geosciences, master's level
Examiners
Note
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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  • apa
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