Abstract
Margarite (end member CaAI2Si2AI2O1O) is reported as nodular aggregates of fine-grained material partly replacing corundum and as fine dispersed material replacing biotite in an inclusion of migmatitic plagioclase-rich gneiss within the Qôrqut granite. Muscovite replaces biotite in the same sample. A retrograde reaction in the presence of volatiles is suggested in which biotite + plagioclase + corundum go to an assemblage containing margarite + muscovite + epidote. Cell parameters and chemical data are presented. A maximum temperature for the reaction of - 5800 at 5 Kb is suggested.
Highlights
During field work in Godthåbsfjord in 1975, centimeter-sized micaceous gray nodules were noted in migmatitic plagioclase-rich gneiss inclusions in the Qorqut Granite Complex near Qupik
The occurrence described in this report for the polymetamorphic gneisses of the Godthåb District appears typical for margarite
Muscovite [theoretical end-member formula: KA(AlzO)VI (Si3 AI)IV 0lO(OH)z] has high MgO and FeO* indicating up to 10% Celadonite component [KA(AIFmO)VI (S4)IV 0lO(OH)z]**
Summary
During field work in Godthåbsfjord in 1975, centimeter-sized micaceous gray nodules were noted in migmatitic plagioclase-rich gneiss inclusions in the Qorqut Granite Complex near Qupik Subsequent laboratory study showed these 'nodules' to be ruby corundum pseudomorphed by margarite. Sample description The sample that was studied (GGU 209465) is a coarse-grained biotite-plagioclase-corundum gneiss.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
